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COPYRIGHT DEPOSIT 



NAVAL ELECTRICIANS' 
TEXT BOOK 



NAVAL ELECTRICIANS' 
TEXT BOOK 



BY 

Lieutenant-Commander W. H. G. BULLARD, U. S. N. 

M 
Head of Departme?it of 

Electrical Engineering, U. S. Naval Academy 

Annapolis , Maryland 




1908 
United States Naval Institute 

Annapolis, Maryland 






UBSARYof CONriRKSSJ 
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Copyright, 1908, by 

Professor PHILIP R. ALGER, U. S. N. 

Sec. and Treas. U. S. Naval Institute 



Vl,%i £or& <$attimon (preee 

BALTIMORE, MD., U. S. A. 



CONTENTS 

CHAPTER PAGE 

I. Derivation axd Definition of Units 9 

II. Resistance 34 

III. Primary Batteries 53 

IV. Types of Primary Batteries 70 

V. Secondary Batteries 75 

VI. Ohm's Law axd its Application to Simple axd 

Divided Circuits 88 

VII. Magnetism axd Electromagxetism 107 

VIII. Electromagnetic Induction 136 

IX. Elementary Theory of the Electric Gen- 
erator 154 

X. Generators . . 176 

XL Efficiencies and Losses of Generators 193 

XII. Dynamo Equations 201 

XIII. Running Generators in Parallel 210 

XIV. Service Generators 217 

XV. Theory of Motors and Motor Control 256 

XVI. Service Motors 290 

XVII. Motor Starting and Controlling Devices. . . 314 

XVIII. Application of Motors 363 

XIX. Principles of Alternating Currents 425 

XX. Dynamo Electric Machines 444 

XXL Tests and Experiments with Dynamo Elec- 
tric Machines 456 

XXII. Motive Power for Generators 499 



8 Contents 

chapter page 

XXIII. Switchboards and Distribution Panels 558 

XXIV. Incandescent Lamps 578 

XXV. Arc Lights 595 

XXVI. Wires 614 

XXVII. Wiring 628 

XXVIII. Wiring Appliances and Fixtures 648 

XXIX. Measuring and Testing 673 

XXX. Measurements 698 

XXXI. Faults of Generators and Motors 724 

XXXII. Tests for and Location of Faults 729 

XXXIII. Telephones 738 

XXXIV. Electrical Interior Communications 762 

XXXV. Care of Electrical Plant and Accessories. . 832 

XXXVI. Principles of Wireless Telegraphy 872 

XXXVII. Principles of Wireless Telephony 915 

Index 933 



bo 

PREFACE 

This book is a revised and enlarged edition of the Naval 
Electricians' Text and Hand Book. Many new chapters have been 
added to the original manuscript and all have been more or less 
J. rewritten and to such an extent that it has lost its hand-book 
characteristics. As stated in the first edition, there is probably 
little or nothing contained in it that cannot be found elsewhere, 
but an attempt has been made to collect complete information con- 
cerning the principles and uses of electricity as applied to our ships 
of war. 

It is primarily intended for use as a text book by midshipmen 
at the Xaval Academy, but officers and the enlisted personnel and 
electricians should find it a fairly complete treatise on electricity 
as far as it relates to the subject of our warship installation. 

It would be difficult to give credit to all those who have made 
suggestions for improvement of the book but special mention should 
be made of the officials of the General Electric Company who have 
contributed many illustrations of the appliances made by them and 
furnished much valuable manuscript. Due credit has been given 
to other manuf? iurers and to those who have allowed the results 
of their experiments to be used. 

W. H. G. BULLARD, 

Lieut. -Commander U. S. Navy. 



CHAPTER I. 

DERIVATION AND DEFINITION OF UNITS. 

All units used in the science of electricity are based on the units 
of the metric system, a system in which certain standards are 
adopted for measuring the three fundamental quantities of length, 
mass and time. 

Standards of the Metric System. 

Length. — The unit of length in the metric system is a metre, 
and was originally intended to be the one ten-millionth part of the 
distance from the earth's equator to the pole measured over the 
surface of the earth along the meridian passing through Paris. 
The present standard of length is the metre, and is the distance at 
0° C. between the ends of a platinum rod preserved in the Archives 
of the French Capital. This distance is slightly less than the 
original measured distance, as the earth's quadrant is now found to 
measure 10,000,880 metres. 

Each metre is equal to 10 decimetres, or 

100 centimetres, or 
1000 millimetres, 
and 1000 metres make a kilometre. 

A metre is 39.37043 inches, or 3.28 feet. 

A decimetre is very nearly 4 inches (3.937 inches). 

A millimetre is very nearly equal to -^ of an inch. 

The kilometre is about f of a mile, or 1093.6 yards. 

Mass. — The unit of mass is the kilogramme, and is equal to the 
weight of the standard kilogramme, a piece of platinum preserved 
with the standard metre in the Archives at Paris. It is intended 
to have the same weight as a cubic decimetre of water at its tem- 
perature of maximum density, 3.9° C. 

The kilogramme is about 2.2 pounds. 



10 Naval Electricians' Text Book 

Time. — The unit of time is the second, and is the n \ -th part 

86400 r 

of a mean solar day. 

C. G. S. (Centimetre, Gramme, Second) System. 

In the C. G-. S. system, the centimetre, — th part of a metre is 

taken as the unit of length; the gramme, ——th part of a kilo- 
gramme is taken as the unit of mass and the second is taken as the 
unit of time. 

Derived Mechanical Units of the C. G. S. System. — There are 
certain mechanical units derived from the three fundamental units, 
such as area, volume, velocity, acceleration, force, work, power, and 
heat. Mechanical and electrical quantities are closely related, and 
in order that the definitions of the electrical units may be under- 
stood, it is first necessary to consider the mechanical units. 

Area. — The unit of area is the square of the unit of length, or 
square centimetre. 

Volume. — The unit of volume is the cube of the unit of length, 
or cubic centimetre. 

Velocity. — The unit of velocity is the velocity of a body that 
moves through unit length in unit time, or it is a velocity of one 
centimetre per second. It is called the kine. 

Acceleration. — The unit of acceleration is the acceleration which 
gives unit velocity in unit time, or an acceleration of one centimetre 
per second in one second. It is called the spoud. 

Acceleration is the rate of change of velocity. If at a certain 
instant a moving body has a velocity V, and at the end of a given 
interval T, it has a velocity V ', its change of velocity has been 
V — V, and the acceleration or rate of change of velocity is 

A- r-y 

A- 7p • 

One of the most common examples of acceleration is that due to 
the attraction of the earth, and bodies falling freely under the 
action of gravity have an acceleration of 32.2 feet per second. This 
means that at the end of each second, its velocity is 32.2 feet per 
second greater than the velocity at the beginning of the second. 






Derivation and Definition of Units 11 

A body falling from rest will fall 16.1 feet in the first second, as 
its acceleration is 32:2 feet, which is its velocity at the end of the 
second, since V = AT and T = 1. The average velocity then is 

and the distance fallen is the time multiplied by the average 
velocity, or 

L = VT — 16.1 X 1 = 16.1 feet. 

At the end of the second second, its velocity has been increased 
by 32.2 feet, or it is now 32.2 + 32.2 = 64.4 feet, and the average 
velocity in the second second is 

T7 32,2 + 64.4 " ■ 

V = s = 48.3 feet, 

and the distance fallen in the second second is 

L — YT — 48.3 feet. 

At the end of the third second, its velocity has been increased by 
32.2 feet, or it is now 64.4 + 32.2 = 96.6 feet, and the average 
velocity in the third second is 

_ 64.4 + 96.6 

V = k = 80.5 feet, 

and the distance fallen in the third second is 
L — YT— 80.5, etc. 
The total distance fallen in three seconds is 

16.1 + 48.3 + 80.5 = 144.9 feet. 
This is also derived as follows: 

Y' — Y = AT and L = ( T ' + 7 ) T, 

or 

L = VT + i AT 2 

in starting from rest Y = 0, or 

L = i AT'-, 
and in the case above 

L = i X 32.2 X 3 2 = 144.9 feet. 



12 Naval Electricians' Text Book 

Examples of Acceleration. 

1. A body travels at the rate of 12 feet per second; in 10 seconds it 
is moving at the rate of 7 seconds per second; what is the mean accele- 
ration? Ans. V 2 ft. per sec. 

2. A body moves in the first second through a space of 16 feet and in 
the fourth second through 112 feet, what is the acceleration per second? 
and how far does it move in the second second and the third second? 

Ans. 32 feet per sec. 
48 feet 2d sec. 
80 feet 3d sec. 

Force. — The unit of force is that force which acting for one 
second on a free gramme mass, will impart to it a velocity of one 
centimetre per second. The unit of force is called the dyne. 

Force is an attribute of matter that produces or tends to pro- 
duce motion or change of motion. Whenever force moves a mass, 
it imparts to it a certain velocity, and if it moves a unit mass with 
a velocity of one centimetre per second in one second it will produce 
unit acceleration and force and mass are thus connected by the 
formula 

F = MA 

the fundamental equation of force. 

There are many kinds of force, such as mechanical, physical, 
electrical, gravitational, etc. It has already been shown how the 
earth's attraction, or force of gravity, acts to produce acceleration, 
and the force with which any body is held to the earth is the pro- 
duct of its mass and the acceleration due to the force of gravity. 
Thus a kilogramme mass is attracted to the earth with a force of 

1000 X 981 = 981,000 dynes. 

The acceleration of gravity is 32.2 feet per second, or since 

1 foot = q-og centimetres, it is 

32.2 X 100 no . . . . , 
— — =981 centimetres per second; 

and since F = MA, the force on one gramme is 
F = 1 X 981 = 981 dynes. 



Derivation and Definition of Units 13 

The unit of force in the English system of units is denned to be 
that force that, if applied to a pound mass for one second, produces 
a velocity of one foot per second. It is called the poundal. 

The force exerted by gravity produces a velocity of 32.2 feet per 
second, and therefore the force exerted on one pound by the force of 
gravity is 

F = MA = 1 X 32.2 = 32.2 poundals. 

Mass is the quantity of matter in a body and weight is a measure 
of the attraction of gravity on the body; thus the weight of one 
gramme is 

F — MA — 1 X 981 = 981 dynes. 

Examples of Force. 

1. A constant force acting upon a mass of 30 grammes causes it to 
move through 10 metres in 3 sees, starting from rest. What is the 
value of the force in dynes? Arts. 6,666% dynes. 

2. Express the weight of 10 kilos, in dynes, and the value of a dyne 
in terms of a grammes weight, g = 981 dynes. Ans. 9,810,000 dynes. 

3. A spring balance is carried in a balloon which is ascending verti- 
cally. What is the acceleration of the balloon when an 8-oz. weight 
hung upon the spring balance is found to indicate 9 oz.? # = 32. 

Ans. 4 ft. per sec. 

4. A body of mass 4 pounds is moving at the rate of 8 feet per 
second. At this instant a constant force begins to act upon it in the 
direction of its motion, and after 20 seconds, its velocity has increased 
to 24 feet per second. Determine the magnitude of the force. 

Ans. 3.2 poundals. 

Work. — The unit of work is the work done in overcoming unit 
force in unit distance, or the work done in overcoming one dyne in 
one centimetre, or the work done by one dyne working through one 
centimetre. It is called the erg. 

Work is done on a body when a force causes it to move or to 
change its direction of motion. A body does work when it over- 
comes another force in a certain distance. Thus a locomotive draw- 
ing a train of cars does work against the friction of the rails, 



14 Naval Electricians' Text Book 

resistance of the air, etc. If the force producing the work is 
removed, if steam is cut off, the train will be brought to rest in a 
certain distance by the force due to the resistances that were pre- 
viously overcome. It is necessary to produce motion in some direc- 
tion for work to be done, however great a force may be applied. 
A locomotive may exert considerable force but unless the train or 
itself is moved, it does no work. 

The English absolute unit of work is the foot-poundal, and is 
the work done by a force of one poundal acting through a distance 
of one foot. 

The practical unit is the foot-pound, which is the work done in 
raising one pound one foot against gravity. Since F = MA, the 
force overcome in raising one pound is F = 1 X 32.2 poundals, and 
the work done is 

W = FL = 32.2 X 1 = 32.2 foot-poundals. 

Therefore, one foot-pound = 32.2 foot-poundals. 

Energy. — Energy is the power of doing work. A body may have 
the power to do work, but yet restrained from doing it. Thus a 
body held at a given distance from the earth's surface has the power 
of doing work and can do so if the restraining force holding it is 
removed. It may fall and do work, as in the case of the hammer of 
a pile-driver. This energy due to its position is called potential 
energy. 

The measure of its potential energy is the amount of work ex- 
pended in putting it in position. Thus, to raise a certain mass M 
to a certain height L, requires work equal to 

W = FL, but F = MA 
and 

W = MAL, or PE = MAL, 

or the body has potential energy equal to MAL. 

If the body falls, the potential energy is converted into energy in 
motion, or kinetic energy, and when it reaches the ground from 
which it was removed, the kinetic energy will be just equal to its 
potential energy at its highest point and will be again equal to the 
work required to raise it. 



Derivation axd Definition of Units 15 

At the moment of striking the ground, it has a velocity V and its 
kinetic energy at that instant is 

KE = ^ MV 2 , derived as follows : 

It has been shown that 

L = iAT 2 and V = AT. 

Therefore, 

PE = 21 AL = M X J x | ^" = i MV ; 

and since the potential energy at its highest point is equal to its 
kinetic energy at its lowest, 

KE = IMV*. 

Examples of Work and Energy. 

1. A body of mass, 3 lbs. is projected vertically upwards with a 
velocity of 640 feet per second; how much work has been done against 
gravity when it has ascended to half its maximum height? 

Ans. 9600 ft.-lbs. 

2. An engine is running at the rate of 80 feet per second on level 
ground, when steam is shut off. Assuming that the frictional resist- 
ances are equivalent to a weight of 14 lbs. per ton, how far will the 
engine run and for how long? Ans. 16,000 feet. 

400 sees. 

3. A 4-oz. bullet is projected vertically upwards with a velocity of 800 
feet per second. What is its potential energy when it has reached its 
maximum height? Ans. 2500 ft.-lbs. 

4. A hammer moving at the rate of 12 feet per second hits a nail and 
drives one inch of its length into a board. The mass of the hammer is 
half a pound. Assuming it to be inelastic, and to come to rest; find 
the average resistance it encountered. Ans. 432 poundals. 

Power. — The unit of power is the erg per second, and is the rate 
of doing work. It is connected with the unit of work by the ele- 
ment of time. Two forces may do the same amount of work in 
different times, and the one that does it in the shorter time is said 
to be the more powerful, that is, it can do more work in a given 
interval of time than the less powerful. If an electric motor can 
turn a turret once completely around in 10 minutes, and another 



16 Naval Electricians' Text Book 

motor can turn the same turret once in five minutes, the second one 
does twice as much work in the same interval of time as the first, 
and it has therefore twice the power of the first one, though they 
each do the same amount of actual work ; they have overcome the 
same force in the same distance. 

The unit of power in the C. Gr. S. system has no distinctive name, 
being called the unit of activity, or the erg per second. 

The practical unit of power in the English system is the horse- 
power, equal to work done at the rate of 33,000 foot-pounds per 
minute, or 550 foot-pounds per second. 

The practical unit of power in the C. G-. S. system is the watt, 
equal to 44.2 foot-pounds per minute. 

Examples of Power. 

1. Find the horse power, H. P., of an engine which will in 9 hours 
empty a vertical shaft of water, whose section is 9 sq. ft. and depth 
400 feet. Density of water == 62.5 lbs. per cubic foot. Ans. 2.525 H. P. 

2. An engine takes a train of 60 tons in all up an incline of 1 in 100 
at a maximum speed of 30 miles per hour and it can take a train of 
150 tons on the level at the same speed. Find the frictional resistances 
of the road in lbs. per ton and the rate in H. P. at which the engine 
works at this speed. Ans. 14.13 lbs. per ton. 

179.16 H. P. 

Heat. — The unit of heat is the amount of heat required to raise 
the temperature of one gramme of water from 0° to' 1° C. It is 
called the calorie. 

The work equivalent to one calorie is equal to 42,000,000 ergs. 

The British unit of heat is the amount of heat necessary to raise 
the temperature of one pound of water 1° F. 

The relation of these units is given under the unit of electrical 
work, the joule. 

Units in the C. G. S. and Practical Systems. 

The underlying principle of these systems of units is the reaction 
of a magnetic field upon a unit magnetic pole. 

A unit magnetic pole is one of such strength that it will repel a 
similar pole with a force of dyne when separated from it one centi- 
metre in air. 



Derivation and Definition of Units 17 

A unit magnetic field is one of such strength that a unit mag- 
netic pole placed in it is acted on with a force of one dyne. It is 
called unit intensity or a gauss. 

The reaction of a magnetic field upon a unit pole only involves 
the terms of force and distance, both of which can be accurately 
measured. 

Unit of Current. 

An electric current is not a tangible material substance ; it cannot 
be seen; a conductor carrying a current looks to be in the same 
condition as one in which no current is flowing. It has certain 
properties; viz., resistance, inductance, and capacity. These de- 
pend upon the material, form, and dimensions of the conductors 
directing the current and upon their relative positions to each other. 
These properties only become manifest when the circuit is sub- 
jected to certain conditions. It will be shown later that electrical 
resistance is only evident when current is flowing ; inductance when 
current is changing, and capacity when electromotive force is 
changing. 

C. G. S. Unit of Current. — An electric current can only be 
detected by the effects produced by it. It may produce sound, light 
or heat, electrolisize certain solutions, or do mechanical work. The 
mechanical work done is due to the reaction of the current and a 
magnetic field. The effect produced by a current of electricity on 
a magnet pole is due, not alone to the current, but in addition (1) 
to the length of the conductor carrying the current; (2) to the 
inverse square of the distance of every element of the conductor 
from the magnet pole ; and (3) to the strength of the magnet pole. 

In order to find the effect of unit current and to satisfy these 
conditions, there must be (1) a conductor one unit in length; (2) 
a conductor every element of which is equally and at unit's distance 
from the magnet pole; and (3) a magnet pole of unit strength. 
To connect these units to the C. G. S. system, the current must be 
directed in a conductor one centimetre long, bent into an arc of a 
circle one centimetre in radius, at the center of which must be 
placed a unit magnet pole. Satisfying these last conditions, if a 
current so strong was made to pass along such a conductor that it 



18 Naval Electricians' Text Book 






acted on the unit magnet pole with unit force, then that current 
would be unit current, that is, one electromagnetic unit. 

We then arrive at the definition of unit current (electromag- 
netic), as follows: The unit of current is one of such strength 
that, if flowing in a conductor one centimetre in length, bent into 
an arc of a circle one centimetre in radius, it exerts a force of one 
dyne on a unit magnet pole placed at the point from which the arc 
is struck. 

A conductor carrying a current and lying in a magnetic field is 
urged with a certain force across the field, the force being propor- 
tional to the length of the conductor and to the strength of the field. 

On this consideration, the C. G. S. unit of current exists when 
each centimetre of its length is urged across a magnetic field of 
unit intensity, or one gauss, with a force of one dyne. 

A unit of one-tenth the value of this C. G. S. unit is called the 
practical unit of current, and is the ampere, being named for Andre 
Marie Ampere, a French physicist who lived from 1775 to 1836. 

A milliampere is a unit one-thousandth of the value of the 
ampere. 

Unit of Quantity of Electricity. 

The unit quantity of electricity is that quantity which is con- 
veyed by unit C. G. S. current in one second. 

The practical unit of quantity is the quantity of electricity con- 
veyed by an ampere in one second. It is equal in value to one- 
tenth the C. G. S. unit of quantity and is called the coulomb, being 
named for Charles Coloumb, a French mathematician, who lived 
from 1736 to 1806. 

Unit of Electromotive Force (E. M. F.). 

If a body is charged with electricity it is said to have a certain 
potential and is capable of doing work. To charge the body work 
must be done on it, and this work can be reproduced by allowing 
the charged body to be connected by a conductor to some other 
body, when its charge will flow along the conductor and do work. 
The more work that is done in charging the body the greater is its 
potential and the more work it is capable of doing. 



Derivation axd Definition of Units 19 

Difference of Potential. — Difference of potential between two 
charged bodies is proportional to the difference of work that has 
been expended in electrifying the bodies. The hammer of a pile- 
driver that has been raised 20 feet has a certain potential energy- 
It has the power to do work depending on its height. A certain 
amount of work has been expended in raising the hammer and this 
work can be reproduced if it is allowed to fall. A similar hammer 
that has been raised 10 feet has also a certain potential energy. It 
has only required half the work to raise it 10 feet as it did to raise 
the one 20 feet. The difference in the heights of the two hammers 
represents the difference in the amount of work they can do, and so 
their potential energies depend on their heights. Similarly, elec- 
tric potentials may be studied by a consideration of their heights 
or difference of levels. 

The amount of work done in the case of each of the hammers is 
measured by the height they have been lifted above the earth's sur- 
face taken as a common level. So it is convenient to regard electric 
potentials as being capable of doing work by the degree that they 
are charged above the potential of the earth, which is regarded as 
a common level, or zero potential. 

Considering as a starting point that the earth is at absolute zero, 
or neutral potential, a body may be so electrified that it is at a 
higher potential than the earth, while another may be at a lower 
potential, depending on the manner they are electrified; or both 
may be so electrified that they are both higher or both lower than 
the earth, and yet be at different potentials. 

Thev each have a certain potential and if connected by a con- 
ducting medium, an electric current would flow from the one of 
higher to the one of lower potential, and equilibrium of potential 
would be established. If the one electrified to a higher potential 
than the earth be called positive, and it is connected to the earth, 
there would be a flow of electricity to the earth. If the one electri- 
fied to a lower potential than the earth be called negative and it is 
connected to the earth, there would be a flow of electricity from 
the earth. In either case, the potential of the earth would not be 
changed. The analogy to this is seen in the level of the ocean, 
which would not be changed if another stream empty into it or a 
well on land is filled from the ocean. 



20 Naval Electricians' Text Book 

Electromotive Force. — Difference of potential may be generated 
in many ways, as by friction, by contact of dissimilar metals, by 
chemical action, or by magnetic induction. In whatever way pro- 
duced, the name electromotive force, E. M. F., is given to express 
the difference of potential generated. 

If a difference of potential exists between two points, a current 
will flow from one point to the other, if they are connected by a 
conducting medium. There will be a gradual fall of potential or 
fall of electric pressure from the one of higher potential to the 
lower. There is a constant endeavor to equalize the difference of 
potential and in doing so, electricity flows from one to the other 
and work is done. If the difference of potential be maintained con- 
stant by the continual expenditure of work there will be a constant 
endeavor to equalization which will result in a continuous flow of 
current of electricity and continuous electric work. 

The constant difference of potential is the total E. M. F. of the 
circuit, whereas between any two points there is a difference or fall 
of potential. The sum of all the differences of potential from one 
point to another around a closed circuit is equal to total fall or 
total E. M. F. 

Fall of potential and total E. M. F. have their analogy in the 
fall of pressure due to a head of water flowing through restricted 
pipes. 

In Fig. 1 represents a tank filled with water and connected by 
the column CB with a level pipe AB, to which are connected verti- 
cal pipes D, E, F, G. The end of the pipe A is fitted with a faucet 
which may be opened or closed, and C is connected to a source of 
supply so that the level of water in C may be kept constant. If 
at first the faucet at A is closed, by a well-known hydrostatic prin- 
ciple, the water will rise in all the pipes until the height in each 
is on the same level and equal to the height in C. The pressure 
along each portion of AB is the same and there is no flow of water. 
This corresponds to an electric conductor AB whose ends are at the 
same potential; that is, there is the same pressure at each end 
and, consequently, there is no difference of potential and no move- 
ment of electricity. 

If now the faucet at A is opened and the consequent difference 



Derivation axd Definition of Units 



21 



of water pressure produced between C and A, water will flow in AB 
and out of each tube, and each level will remain at a height which 
is determined by the pressure in each tube. If now water is 
poured into C as fast as it flows out from A, the level of the water 
in the several tubes will remain stationary, while the flow of water 
through BA will be constant. Experiment will show that if the 
cross-section of AB 'is uniform and the tubes are equally spaced 
from each other there will be an equal difference in the levels of the 
tubes, and the fall of pressure may be shown by a straight line 
connecting the level of the water in C and end of tube A. The 




Fig. 1. — Illustrating Fall of Potential. 



fall of water pressure is due to the friction of the sides of the pipe 
BA and the fall of pressure is expended in overcoming this 
resistance. 

This is the case of a conductor whose ends are at different poten- 
tials. The level in C represents the total E. M. F. in the circuit 
and is kept up b}' the expenditure of work necessary to keep the 
height of the water at a constant level. In 6ach section of BA 
there is a drop or fall in potential, and the sum of all the differ- 
ences from B to A is equal to the total E. M. F., represented by the 
total head of water. The fall of potential is expended in over- 
coming the resistance of the conductor, just as the drop in water 
pressure was expended in overcoming the friction to the pipe. 



22 Naval Electricians' Text Book 

If the cross-section of AB is not uniform, the water will stand 
at different heights such that the fall of the pressure between them 
will not be regular. The different sections will then offer different 
amounts of friction, so the fall in pressure will be greater or less. 
And in the case of the electric conductor, if the resistance through 
any one particular section is great, the fall of potential will be 
great. However, whatever the area of cross-section, the same 
amount of water will flow through each section, flowing more 
rapidly in the smaller sections, and in the electric current, what- 
ever the resistance, the same amount of current flows through each 
part of the circuit. 

C. G. S. Unit of E. M. F. — Of all the means available for gener- 
ating E. M. E. that by magnetic induction seems the most logical 
one on which to base a consideration of the definition of the unit 
E. M. E. and the one which follows most closely the theoretical 
conditions. 

It is an experimental fact that when a conductor is moved across 
a magnetic field there is produced in it a tendency to set up an 
induced E. M. E. 

A magnetic field is a space or region surrounding magnetic 
substances, either permanent or temporary, in which magnetic force 
acts; a space filled with so-called lines of force, which by their 
number at any one place represents the quantity or amount of force 
and by their direction, the resultant direction of the magnetic force. 

The C. G-. S. unit of electromotive force is denned to be that 
E. M. F. produced by the cutting of a magnetic field of one gauss 
intensity by one centimeter of the conductor moving at a velocity 
of one centimeter per second. 

A unit one hundred millions times the value of this C. G. S. unit 
is called the practical unit of E. M. F. and is the volt, being named 
for Alessandro Volta, an Italian physicist who lived from 1745 
to 1827. 

A millivolt is a unit one-thousandth of the value of the volt. 

Unit of Resistance. 

The application of a steady E. M. E. to the ends of a conductor 
will produce in the conductor a current inversely proportional to 






Derivation axd Definition of Units 23 

the resistance the conductor offers to the flow of electricity. A con- 
ductor has one electromagnetic unit of resistance when a steady 
E. M. F. of one electromagnetic unit applied to it produces one 
electromagnetic unit of current. This definition is derived from 
a consideration of Ohm's law. 

Ohm's Law. — This law expresses the relation between E. M. F. 
current and resistance in a closed circuit in which the current is 
continuous. It states that the current is directly proportional to 
the E. M. F. and inversely proportional to the resistance, or in 
symbols, 

c- E 

where 

C = Current, 
E = E. M. ¥., 
R = Kesistance. 

This relation holds in whatever system of units the quantities are 
expressed, provided they are all expressed in the same system. This 
law will be more fully dealt with later, and is only introduced here 
to help explain the unit of resistance. A consideration of the 
relation existing between the electromagnetic units of current and 
E. M. F. and the practical units shows that the ohm must be of a 
value 1,000,000,000 times as great as the electromagnetic unit of 
resistance. In both systems of units by Ohm's law 

r\ E 

where C, E, and R represent current, electromotive force, and re- 
sistance in the two systems. If C", E' , and R! represent the values 
in the practical system of units and C" , E" , and R" the values in 
the electromagnetic system, we have 

C" = 10- 1 &, 
E' = 10 8 E", 

E' ," E" 



whence 



R! — ^-and R" = jp, 



10 8 E n 10 8 

R! = yyijpr or R' = -jqj R" — 10 9 R" ; 



24 Naval Electricians' Text Book 

or, in practical units, the ohm, the unit must be 10 9 times as great 
as the value of the electromagnet unit. 

A unit 1,000,000,000 times the value of the C. G. S. unit of 
resistance is called the practical unit of resistance and is the ohm, 
being named for George Simon Ohm, a German mathematician who 
lived from 1789 to 1854, and who was the first to clearly enunciate 
Ohm's law. 

A megohm is a unit one million times as great as the ohm. 

A microhm is a unit one-millionth of the value of the ohm. 

Unit of Power. 

The C. G. S. unit of power is denned as the rate at which work is 
being done when one C. G. S. unit of current works under a pressure 
of one C. G. S. unit of E. M. F. 

The practical unit of power has a value ten millions times as 
great as the C. G. S. unit of power and is called the watt. 

The watt is defined as the rate at which work is being done when 
a current of one ampere works under a pressure of one volt and is 
sometimes referred to as the volt-ampere. 

To connect the watt with the C. G. S. units of power, it is only 
necessary to substitute the values of the volt and ampere in terms 
of the C. G. S. units of electromotive force and current, thus 

1 watt = 1 volt X 1 ampere 






and 



or 



1 volt = 10 8 C. G. S. units of E. M. F., 
1 ampere = 10 _1 C. G. S. units of current, 



1 watt = 10 8 X 10" 1 = 10 7 C. G. S. units of power. 

Considering how work in mechanics is defined as the product of 
a force and the distance moved through due to this force, it is easy 
to trace the analogy to the derivation of the watt. This is seen in 
the mechanical work performed by a ventilating fan, the difference 
of pressure between the entering and leaving orifices forming a 
current. of air, and its power to do work is measured by the differ- 
ence of pressure produced, and the rate of the moving current of 
air. The difference of pressure at the orifices corresponds to the 



Derivation and Definition of Units 25 

difference of potential of the current, and the air current to the 
electric current, and their product is the power of the fan, or its 
rate of doing work. In this connection, it must be recalled that the 
ampere is not the quantity of current, but rather the rate of flow 
or quantity in unit time. The total work done in any time would 
be the number of watts multiplied by the time in seconds. 

In order to connect mechanical and electrical units of power, it 
is sufficient to remember that one mechanical horse-power is equal 
to 746 watts. This is derived as follows : 

1 H. P. = 33,000 ft.-lbs. per minute, 
— 550 ft.-lbs. per second, 
1 ft. = 30.48 centimetres, 
1 lb. = 453.7 grammes, 
1 ft.-lb. = 30.48 X 453.7 = 13,828.77 gramme-centimetres. 

A gramme-centimetre is the work done in raising one unit of 
mass, one gramme, one centimetre against the force of gravity. 
The work done must be the product of force overcome and the dis- 
tance through which it is overcome. The average force of gravity 
per unit mass of 1 gramme is 981 dynes, and the work done in 
lifting 1 gramme 1 centimetre against this force is 981 dyne- 
centimetres. In the derived mechanical units of the C. G-. S. 
system, the dyne-centimetre is called the erg. So when 1 gramme 
is lifted 1 centimetre against gravity, the work done is 981 ergs, 
or in other words, 1 gramme-centimetre is equal to 981 ergs. 

1 ft.-lb. = 13,828.77 X 981 ergs 
= 13,566,029 ergs, 
or 

1 H. P. = 550 X 13,566,029 = 7,461,351,900 ergs per second. 
The erg per sec. = the C. Gr. S. unit of power, 

1 H. P. = 746 X 10 7 C. G. S. units of power, 
1 watt = 10 7 C. G-. S. units of power, 
or 

1 H. P. = 746 watts. 

The watt was named for James Watt, an English physicist, the 
inventor of the steam engine, who lived from 1736 to 1819. 



26 



Naval Electricians' Text Book 



A unit one thousand times as great as the watt is the kilowatt. 



To convert 


Multiply by 


Divide by 


Watts into H. P. 


.00134 


746 


tt ( 


ergs per sec. 


10 7 




a i 


ft.-lbs. per min. 


44.2 




<( i 


ft.-lbs. per sec. 


.737 




U i 


kilogr.-metres per 


sec. .102 


9.8] 


H. P. < 


ft.-lbs. per min. 


33.000 




a i 


ft.-lbs. per sec. 


550 




a a 


kilowatts 


.746 




a i 


watts 


746 




U i 


ergs per sec. 


7.46 X 10 9 






Unit of Work. 





The C. G. S. unit of work has already been defined. The prac- 
tical unit of work is a unit 10,000,000 times as great as the C. Gr. S. 
unit and is called the joule, being named for James Prescott Joule, 
an English physicist, who lived from 1818 to 1889. As heat and 
work are mutually convertible, it is sometimes referred to as the 
electrical unit of heat and is equal to 10,000,000 ergs. Ptemember- 
ing that the watt is the unit rate of doing work, the number of units 
of work, or joules, performed in a given time, must be equal to the 
number of watts multiplied by the number of seconds. The watt 
was shown to be equal to one volt times one ampere, or 

W = C X E, 
and multiplying by t, we have 

j = cm. 

If t = 1 second, the watt is equal to the joule, or the watt may 
be defined as the work done at the rate of one joule per second. 
Substituting for E, its value by Ohm's law, E = CR, 

J = C 2 Rl 

When C, R, and t are all unity, J is unit}', and remembering 
that the joule is the unit of work, expressed as heat, it may be 
defined as the heat developed in a conductor in one second by a 
current of one ampere flowing through a resistance of one ohm. 



Derivation and Definition of Units 27 

The mechanical work equal to one heat unit in the English sys- 
tem of units, for 1° P. is taken to be 778 ft.-lbs., this number being 
determined by experiment. This means that 778 ft.-lbs. of work, 
if converted into heat, would raise the temperature of 1 lb. of water 
at 39° + F. through 1° F. This number 778 expressed in degrees 
Centigrade becomes 

|- X 778 = 1400 ft.-lbs., 

. 1400 

or m metric units q-qh = 42 7 kilogramme-metres. 

This number 427 kilogramme-metres represents the amount of 
work done equivalent to the work expressed in heat, necessary to 
raise the temperature of one kilogramme of water at 4° C. to 5° C. 
and this value expressed in gramme-centimetres is 42^700. 

These figures follow from the consideration that 

9 
'No. of degrees F.° = -g- no. of degrees C.° + 32, 

1 f t = 3^8 metre > 

and 

1 cm. = ^a?) metre. 

In the change of units from one system to another, it is not 
necessary to consider the change in the unit of mass, as the mass 
of water that is raised in temperature changes in the same ratio. 

Under the watt, it was seen that 1 gr.-cm. was equal to 981 ergs, 
and therefore the mechanical equivalent in the C. G-. S. system is 

42,700 X 981 = 4.18 X 10 7 ergs 
= 4.18 joules. 

As the watt is equal to CE or C 2 R, and the calorie is equal to 
4.18 joules, we have the relation 

1 calorie = 4.18 X C 2 R 
= 4.2 joules, 
or 

1 joule 3= .24 calorie. 

This expression is an important one for calculating the rise of 



28 Naval Electricians' Text Book 

temperature of conductors due to currents flowing in them. The 
rise in temperature 0° is calculated from the formula 

co , n 4. x .24 X C 2 Rt 

(Cent.) = 

where C, B, and t retain their usual significations, and 
m = mass of conductor in grammes, and 
s = its specific heat. 



To convert 

Watts into B. T. IT. per sec. 


Multiply by 

.000954 


Divide by 

1,048 


" " joules per sec. 
H. P. " calories per sec. 


1 

179.4 




" " B. T. U. per sec. 


.72 





1 H. P. = 33,000 ft.-lbs. per min., and is also equal to 746 watts ; 

therefore, 

. , , 33000 , . _ „, ■ • 

1 watt =: -ifjrr- = 44.2 ft.-lbs. per mm., 

and the watt being the work at the rate one joule per sec. 

44 2 
1 joule = ^ = .737 ft.-lbs. 

The work in ft.-lbs. done by a current of C amperes flowing 
through B ohms for t minutes is 

W = 44.2 C 2 Bt ft.-lbs. 

The number of calories produced by a current C, in resistance B, 
in time t is 

H = .24 C 2 Bt. 

The number of B. T. TJ. produced by a current C, in resistance B } 
in time t is- 

H 1 = 6 ° 1 ^Q 24 C 2 Bt = .0316 C 2 BL 
453.9 

The number of joules produced by a current C, in resistance B, 

in time t is 

joules == C 2 Bt and 

watts = C 2 B or, since CB = E, 

watts == CE. 



Derivation and Definition of Units 29 

1 calorie = 4.18 joules 

= 4.18 X 10 7 ergs = 3.086 ft.-lbs. 

= .00396 B. T. IT., 

IB. T. U. = 252 calories 

— 1060 joules = 1060 X 10 7 ergs 

— 777.7 ft.-lbs., 

1 joule = .239 calorie 

= 1 watt per second- 
Examples cf Power, Work, and Eeat. 

1. If 20 amperes flow through a circuit of 10 ohms resistance for an 
hour, find (1) the heat generated (2) work done in the circuit (3) 
power absorbed. Ans. 3,441,600 calories. 

14,400,000 joules. 
321.6 H. P. 

2. What will be (1) the heat generated (2) work done in a circuit 
in which a current of 100 amperes causes 50 electrical horse power to 
be absorbed in 1 hour. Ans. 534,882 calories. 

2,238,000 joules. 

3. Find the potential difference at the terminals of a circuit in which 
10 H. P. is absorbed, when a current of 37.3 amperes passes through it. 

Ans. 200 volts. 

4. An incandescent lamp of 145 ohms resistance is placed under water 
in a pail containing 2 kilos of water at 18° C. How long must a current 
of 2 amperes flow through the lamp in order to raise the temperature 
of the water to 35° C, provided 98# of the heat goes to raise the tem- 
perature of the water. 

Calories generated = .24CFRt (1) 

Calories required = (35-18) X 2000 (2) 

34000 

(l) = (2)or t=. = 249.2 s = 4.15 min. 

2 2 X 145 X .24 X .98 

5. How much paraffin could be raised in temperature from 10° C. and 
melted in four minutes by a current of 3 amperes through a wire of 
12 ohms resistance imbedded in the paraffin. Ap. heat of paraffin = .2, 
latent heat = 8, melting point 54° C. 

Heat generated in calories = (PRt X .24 

= 9 X 12 X 4 X 60 X .24 (1) 

Heat necessary =M X .2 X (54-10) +1X8 (1) 

(1) = (2) or M= 370.3 grams. 



30 Naval Electricians' Text Book 

Unit of Capacity. 

When an E. M. F. is applied to the terminals of a condenser a 
certain quantity of electricity will flow into it nntil it is charged 
to the same potential as the applied E. M. F. For the present, a 
condenser may be considered as simply two plates of conducting 
materials separated by an insulating plate. 

In charging such a condenser, current will flow into it only as 
long as the E. M. F. at its terminals is changing, and a definite 
change will allow a definite quantity to be held in the condenser. 
The quality of being able to store this energy is called the capacity 
of the condenser. 

The capacity is defined either in terms of the quantity of elec- 
tricity which can be held at a certain potential, or in terms of the 
current which will flow into the condenser when the difference of 
potential is changing at a certain rate. 

A circuit or condenser has a capacity of one C. Gr. S. unit of 
capacity when a rate of change of potential of one C. G. S. unit of 
E. M. F. per second produces one C. 67. S. unit of current, or a 
condenser has unit capacity when it is charged to a potential of one 
C. G. S. unit by one C. G. S. unit of quantity of current. 

The practical unit of capacity is a unit one one-thousand-mil- 
lionth, 10" 9 , of the value of the C. G. S. unit of. capacity, and is 
called the farad, being named for Michael Faraday, a celebrated 
English physicist, who lived from 1791 to 1867. A condenser to 
have the capacity of the farad would be extremely large and a 
working unit has been adopted, called the microfarad, which is one- 
millionth of a farad. 

It may be said that the potential is directly proportional to the 
charging current and inversely proportional to the capacity. The 
less the capacity the higher will be the potential for a given current 
and vice versa. 

Example of Capacity. 
The E. M. F. in a circuit alternates between 20,000 volts positive and 
negative, 40 times a second. What current will flow in a conductor if 
its capacity is 8 microfarads? Ans. 12.8 amperes. 



Derivation axd Definition or Units 31 

Unit of Inductance. 

Inductance is the property of an electric circuit by which it re- 
sists a change in the current. When a rate of change of current of 
one C. G. S. unit per second induces an E. M. F. of one C. G. S. 
unit, the circuit has unit inductance. 

It will be shown that every circuit carrying an electric current 
is surrounded by a magnetic field, which is brought into existence 
by the current. Any change in the current will produce a change 
in the magnetic field, and this field reacting on the conductor in- 
duces an E. M. F. which tends to prevent any change. If the 
current is increasing, the induced E. M. F. tends to prevent the 
increase, and similarly when decreasing the induced E. M. F. tends 
to prevent the decrease. 

The induced E. M. F. is directly proportional both to the rate of 
change of current and to the inductance. The induced E. M. F. 
acts as a counter E. M. F. to the applied E. M. F. producing the 
current. If a certain current is flowing in a circuit of certain in- 
ductance, the E. M. F. required to reverse it in a given time may 
be calculated. 

The practical unit of inductance is a unit of one-thousand mil- 
lions, 10 9 times as great as the C. G. S. unit of inductance, and is 
called a henry, being named for Joseph Henry, an American 
physicist, who discovered many of the laws of magnetic induction. 

Examples of Inductance. 

1. The current in a circuit is changed from to 50 amperes in .005 
second. The average induced E. M. F. is 10 volts. What is the induct- 
ance of the circuit? Ans. 1 Millihenry. 

2. How many average volts are required to reverse a current of 50 
amperes in a circuit of 5 henries inductance in .5 of a second? 

Ans. 1000 volts. 

International or Legal Units. 

As a result of an International Congress of Electricians held in 
1893, the following units were adopted, these being approved and 
adopted in June, 1894, by the United States Congress : 

1. The unit of resistance, the international ohm, which is based 



32 Naval Electricians' Text Book 

upon the ohm equal to 10 9 units of resistance of the C. G. S. system 
of electromagnetic units, and is represented by the resistance 
offered to an unvarying electric current by a column of mercury at 
the temperature of melting ice, 14.4521 grammes in mass, of a 
constant cross-sectional area, and of a length of 106.3 centimetres. 
If the mass of one cubic centimetre of water at 4° C. is one 
gramme, the area of cross-section of such a column will be one 
square millimetre. 

2. The unit of current, the international ampere, which is 10 -1 
of the unit of current of the C. GL C. system of electromagnetic 
units, and which is represented sufficiently well for practical use 
by the unvarying current, which, when passed through a solution of 
nitrate of silver, in water, and in accordance with standard specifi- 
cations, deposits silver at the rate of .001118 gramme per second. 

The anode in the solution is pure silver, the kathode pure plati- 
num, and the liquid is a neutral solution of pure silver nitrate, 
containing about 15 parts by weight of the salt to 85 parts by 
weight of water. 

3. The unit of electromotive force, the international volt, which 
is the E. M. F. that steadily applied to a conductor, whose resist- 
ance is one international ohm, will produce a current of one 
international ampere, and which is represented sufficiently well 

for practical use by .. q of the E. M. F. between the poles or 

electrodes of the voltaic cell known as Clark's cell, at a tempera- 
ture of 15° C. and prepared in a manner according to standard 
specifications. 

The Clark's cell consists of zinc and mercury .in a saturated 
solution of zinc sulphate (ZnS0 4 , 7H 2 0) and mercurous sulphate 
in water, prepared with mercurous sulphate in excess, all held in a 
small glass jar. The E. M. F. is determined at any temperature 
t° C. by the formula 

# = 1.4342 [1 — .00077 (/— -15)]. 

4. The unit of quantity, the international coulomb, which is 
the quantity of electricity transferred by a current of one interna- 
tional ampere in one second. 






Derivation and Definition of Units 33 

5. The unit of capacity, the international farad, which is the 
capacity of a conductor charged to a potential of one international 
volt by one international coulomb of electricity. 

6. The unit of work, the joule, which is 10 7 units of work in 
the C. G. S. system, and which is represented sufficiently well for 
practical use by the energy expended in one second by an inter- 
national ohm. 

7. The unit of power, the watt, which is equal to 10 7 units of 
power in the C. G-. S. system and which is represented sufficiently 
well for practicaluse by the work done at the rate of one joule 
per second. 

8. The unit of induction, the henry, which is the induction in 
the circuit when the E. M. F. induced in this circuit is one interna- 
tional volt, while the inducing current varies at the rate of one 
ampere per second. 



CHAPTEK II. 
RESISTANCE. 

All kinds of matter, whether solid, liquids, or gaseous, offer a 
resistance to the passage of electricity. An electric current cannot 
flow unless a difference of electric potential exists, nor can a cur- 
rent flow without encountering some resistance. The definition of 
the International Unit of Resistance, the ohm, is based on the fact 
that a certain column of mercury at a certain temperature has a 
given definite resistance, or it offers at that temperature a certain 
obstruction to the passage of electricity. 

Those substances which offer little resistance to electric currents 
are called conductors, and those which offer great resistance are 
called insulators. Between these extremes are certain substances 
which are partly conductors and partly insulators and which are 
called partial conductors. 





Table of Conductors. 






Good Conductors. 




Silver, 


Lead, 


Manganin, 


Copper, 


Mercury, 


Brass, 


Aluminum, 


Carbon, 


Bronze, 


Zinc, 


Water, 


Phosphor Bronze 


Platinum, 


German Silver, 




Iron, 


Platinum Silver, 
Partial Conductors. 




The Body, 


Cotton, Dry wood 


, Paper. 



Uses of Conductors. 

Most of these conductors find some use in the electrical apparatus 
and instruments installed on board ship. 

Copper is used in the dynamo and motor windings, electric light 



Eesistaxce 35 

and power mains, switchboards, bus bars, switches, interior com- 
munication circuits, and in general where high conductivity is 
required and full of potential small. It is particularly adapted for 
conductors on account of its high conductivity, its abundance, and 
the ease with which it is worked into various shapes. For con- 
ductors it is generally of the wire, ribbon, or bar shape. 

Zinc finds its principal use in the anodes of electric batteries. 

Platinum conductors are used in incandescent lamps as connect- 
ing wires between the copper leading wires and the carbon fila- 
ments. Alloys of platinum are used in some forms of rheostats. 

Brass or bronze finds use for conductors on switchboards, and in 
the various terminals of dynamo leads on headboards and switch- 
boards and as the interior fittings in water-tight appliances. The 
conductors, however, for these are copper. 

Lead or an alloy of lead is used for conductors in the numerous 
fuses placed in different parts of dynamo or motor circuits to pro- 
tect the circuits against excessive current. 

Carbon is used for conductors in dynamo and motor brushes, in 
contact pieces for circuit breakers and in the searchlights and arc 
lamps. 

Manganin is used in the resistances of voltmeters and ammeters. 

German silver finds use in rheostats, resistance coils, and parts 
of apparatus where high resistance is required. Its general com- 
position is : 

Copper 4 parts. 

Nickel 2 parts. 

Zinc 1 part. 

The variation of the resistance of German silver due to changes 
of temperature is very small, its coefficient per degree rise in tem- 
perature C.° being about nine times less than that of copper. 
Strong currents continually used in German silver resistances tend 
to make the conductors brittle. 

Phosphor bronze is used in the clips of switches to prevent 
blisters forming, due to the arc on opening the switch. In some 
cases it has been used for commutator segments, but they are 
usually now made of hard drawn copper. 



36 Naval Electricians' Text Book 

Laws of Resistance. 

Experiment shows that the two following laws hold in the case 
of conductors : 

First Law. — The resistance of a given conductor of uniform sec- 
tion at a constant temperature is directly proportional to its length. 

Thus if I represents length and R resistance, then R varies 
directly as I, or 

Roc I 

If a conductor of a certain length has a certain resistance, then 
a conductor twice as long, of the same area of cross-section, at the 
same temperature, will have a resistance twice as great; and if half 
as long, it will have a resistance half as great. 

Second Law. — The resistance of a given conductor at constant 
temperature is inversely proportional to its sectional area. 

If, as before, R represents resistance and a area of cross-section, 
then R varies inversely as a 

22 oc 1. 

a 

If a conductor of a certain area of cross-section at a certain tem- 
perature has a certain resistance, then a conductor of twice the area 
of cross-section, at the same temperature, will have a resistance one- 
half as great; and if half its area of cross-section, it will have a 
resistance twice as great. 

From a consideration of the above laws, it is seen that, R varies 
directly as the length and inversely as the area of cross-section of 
the conductor, or 

RozL. 
a 

In order that this equation may give the value of R in ohms and 
be a pure equation rather than a proportion, it is necessary to 
multiply it by a constant for the particular material of the con- 
ductor and temperature at the time. 

This constant is called the specific resistance of the conductor at 
the temperature and is defined as the resistance in ohms of unit 
length of the conductor having unit cross-sectional area. 

The unit adopted is both the inch and the centimetre, so that the 



Resistance 37 

specific resistance is the resistance in ohms per cubic inch or per 
cubic centimetre of the conductor, or it is the resistance in ohms 
between the opposite faces of a cube, either one inch or one centi- 
metre on the side. 

Combining the laws of resistance with the definition of specific 
resistance, we have the fundamental equation of resistance 

R = P 1 (1) 

Li 

where p represents the specific resistance of the conductor at a cer- 
tain temperature. 

Thus the resistance of any conductor may be found if its specific 
resistance, length, and area of cross-section is known. 

In cases where it is inconvenient to measure the length, as in a 
long coil, it mav be weighed and / found from the expression 

where w = weight in grammes, 

a = area in sq. cm., 

d = specific density, 
R then becomes, by substituting the value of I from (2) in (1) 

a 1 a 
The specific resistance is usually stated in microhms; thus, that 
of lead is 19.63 microhms, or .00001963 ohms expressed in C. G. S. 
units. 

Table of Specific Resistances. 

Substance at 0° C S P- resist - microhms- Relative 

ouDStanceatu u. per cm. cube. Conductivity. 

Copper (annealed) 1.57 100 

Copper (hard) 1.60 98 

Silver 1.49 105 

Platinum 8.98 17 

Iron 9.638 16 

Lead 19.63 8.3 

Mercury 94.34 1.6 

Carbon (arc light) 4000 -JL- 

German Silver 20.76 7.6 

Platinoid 30 to 36 

G,asS •-:• aiXlO-lessthan ^^ 

Gutta-percha 4.5 X 10 20 same. 



38 Naval Electricians' Text Book 

Table of Resistances of Chemically Pure Metals at 0° C. in 
International Ohms. 

Resist, of a wire Resist, of a wire 

Name of metal. l«.longj4" Serein 

in diameter. diameter. 

Silver, annealed 9.0283 .01911 

hard drawn 9.8028 .02074 

Copper, annealed 9.587-7 .02029 

bard drawn 9.8068 .02075 

Gold, annealed 12.3522 .02614 

hard drawn 12.5692 .0266 

Aluminum, annealed 17.4825 .037 

Zinc, pressed 33.7614 .07145 

Platinum, annealed 54.3517 .11503 

Iron, annealed 58.308 .12342 

Lead, pressed 117.79 .24921 

German Silver 125.6139 .26588 

Platinum Silver 146.3621 .30979 

German silver, an alloy of copper, nickel, and zinc, combined with 
1 to 2 per cent of tungsten is known as platanoid. The additioi 
of tungsten gives the alloy greater density and reduces tendency to 
oxidation. The alloy takes a polish like silver. 

Any foreign matter considerably reduces the conductivity of 
metals and alloys usually show higher resistances than any of 
their constituents. As a rough unit, a mile of copper wire, J" 
diameter has a resistance slightly less than one ohm. 

Relation of Heat and Resistance. 

Generation of Heat. — One effect of a current of electricity on a 
conductor is to produce heat in the mass of the conductor, the 
number of joules developed being given by the equation C 2 Rt. The 
greater the current, the higher the resistance and longer the time, 
the greater the increase of heat and consequent rise of temperature. 

If the heat is carried away by conduction or radiation as fast 
as developed its* temperature will not rise; or, if after a certain 
temperature has been attained, the heat is carried away as fast as 
developed, the conductor will remain at that temperature; but if 
the heat cannot be dissipated, the conductor will get hotter and 
hotter until its melting point is reached. 



Resistance 39 

Table of Melting Points. — The melting point of some of the most 
important conductors are in degrees C. 

Alloy, 3 lead, 2 tin, 5 bismuth 93° 

Alloy, iy 2 tin, 1 lead 168° 

Alloy, 1 tin, 1 lead 240° 

Tin 230° 

Lead 325° 

Aluminum 625° 

Bronze 922° 

Silver 945° 

Gold 1045° 

Copper 1054° 

Cast Iron 1135° 

Steel .1380° 

Steel, hard 1410° 

Wrought iron 1600° 

Platinum 1775° 

The current that will melt copper wire is given by the formula 

C = 80dt 



where 



or 



where 



C = current in amperes, 

d = diameter of conductor in millimetres, 

C = Modi 



d = diameter in thousandths of an inch. 

The diameter in inches of a lead conductor that will melt with 
a given current is equal to the cube root of the square of the 
quotient of amperes divided by 1379. For half and half solder 
the divisor is 1318. 

Variation of Resistance with Temperature. — It is to be noted 
that the table of specific resistances is for materials at a certain 
temperature, 0° C. This is necessary from the fact that the resist- 
ance of any substance, conductor or insulator, depends on the 
temperature at any given time. 

The resistance of all the metals, and with few exceptions of all 
the alloys, increases with rise of temperature. Non-metals, such as 



40 Naval Electricians' Text Book 

the solids, carbon, sulphur, silicon, phosphorus, etc., and the prin- 
cipal gases, oxygen, hydrogen, nitrogen, chlorine and its family all 
decrease in resistance for a rise of temperature. Also the resist- 
ance of liquids that can be electrolyzed decreases for a rise of 
temperature. 

Resistance Temperature Coefficient. — The resistance temperature 
coefficient is defined to be the amount of increase or decrease of 
resistance in ohms which one ohm in any substance would undergo 
for each degree Centigrade change of temperature. 

The resistance of conductors increases with temperature in 
accordance with the following empirical formula : 

R = r(l + at±bt 2 ) 
where 

R = resistance at temperature t, 
r = resistance at temperature 0° C, 
t = temperature in degrees C, 
a, b = temperature coefficients of the conductor. 

It is usually sufficient to disregard the last term and use 

R = r(l+at). (a) 

It is ordinarily sufficient to regard t as the difference between 
any two temperatures, and then r becomes the resistance at the 
lower and R at the higher temperature. 

The temperature coefficient a is positive for all elementary metals 
except carbon and for most pure metals has an average = .004 be- 
tween 0° C. and 100° C. 

As a general rule, if two or more elements form an alloy, it has a 
higher specific resistance and lower temperature coefficient than 
any of its component elements. 

The increase in temperature of copper conductors, apart from the 
increased resistance, is an important factor in calculating the size 
of conductors to carry certain currents, as they must be large 
enough to carry their currents with overheating. 

Formula (a) may be used to determine the increase in tempera- 
ture of conductors due to current, by measuring the resistance both 
when hot and cold. Then knowing the temperature coefficient, the 
increase in temperature t may be calculated. 



Rt — - . 



Resistance 41 

The effect of a change in temperature shows that it is important 
to know the resistance of certain conductors when current is flow- 
ing, as the different windings of dynamos and ^motors, of rheo- 
stats, regulators and starting boxes, and particularly it is required 
to know the hot resistance of incandescent lamps, so that the cur- 
rent a lamp is absorbing when it is giving its rated candle-power 
may be known. 

Temperature Correction for Copper Conductors. — A simple for- 
mula for finding the resistance of a copper conductor at any tem- 
perature is given below. 

LK 

d l 
where 

Et = resistance at temperature t, 
L = length of conductor in feet, 
d = diameter of conductor in mils, 
d 2 =. area of conductor in cir. mils, 
K = a calculated constant 

K is given in the following table for certain temperatures ; the 
temperatures being calculated from assumed values of K, this being 
the resistance in ohms of one mil-foot, assuming that the resistance 
of one mil-foot of pure copper wire is 9.162 ohms at 0° C. 

Resistance per mil-foot Temperature, 

in ohms K. degrees Centigrade. 

10.00 10.26 

10.10 12.86 

10.20 15.44 

10.30 18.00 

10.40 20.54 

10.50 23.06 

10.60 25.56 

10.70 28.04 

10.80 30.50 

10.90 32.95 

11.00 35.38 

11.10 37.80 

11.20 40.20 

11.30 42.58 

11.40 44.95 

11.50 47.30 



42 Naval Electricians' Text Book 

If the temperature is given in degrees Fahrenheit, it must be 
reduced to degrees Centigrade by using the formula 

Thus suppose it was required to find the resistance at 64.4° F. 
of 100 feet of copper wire 4000 cir. mils in area. First reduce 
64.4° F. to degrees C. thus 

C=-y (G4.4 — 32) =18°. 
The value of K corresponding to 18° C. is 10.30, so 

R = 4^ X 10.30 = .2575 ohm. 

The value of K to be used in the formula is the one that corre- 
sponds most nearly to the given temperature ; or the exact value for 
any temperature may be found by interpolation. 

Suppose we want to find the value of K corresponding to t = 36° 
C. The difference in K for a difference of 37.80 — 35.38 = 2.42 

t is (11.10 — 11.00) = .1 or for 1* it is ^ and for (36 — 35.38) 

62 V 1 

= .62t the difference is 040' — -0256, which added to the value 

of K for 35.38° becomes 11.0256. 

Problems on Resistance. 

1. Find the resistance at 25° C. of a copper wire 10 metres long and 
1 mm. in diameter. The resistance of copper increase by .39$ for each 
degree rise of temperature. Sp. resistance of copper = 1600 C. G. S. 
units. 

R =p~ = 1600 X - ° * 10Q X j-^pr= 2.037.8 X 10 s C. G. S. units 

2.0378 X 10 8 OAOr7 v 
or R = jQ9 =.2037 ohm 

i?, 5 o=.2037 (1 + 25 X .0039) =.2236 ohm. 

2. A uniform glass tube 92.1 cm. in length was filled with mercury 
and the resistance of the column of mercury was measured and found 
to be 1.059 ohms. The weight of the mercury contained in the tube 
was 10.15 grms. Calculate from this experiment the specific resistance 
ot mercury, taking its specific gravity as 13.6. 

Ans. 93177 C. G. S. units 



Resistance 43 

3. The resistance of a bobbin of wire is measured and found to be 
68 ohms; a portion of the wire 2 metres in length is now cut off and its 
resistance is found to be .75 ohm. What was the total length of wire 
on the bobbin? 



JTT 



B=P^3=68 R'= P —, = .15 



I 68 _ 200 X 68 _ 1C1 o mofrM 

or -jt = -~- Z = — ~f =181.3 metres. 

I .70 7o 

4. The resistance at 0° C. of a column of mercury 1 metre in length 
and 1 sq. mm. in cross-section is called a " Siemens unit ". Find the 
value of this unit in terms of the ohm. Sp. resistance of mercury = 94,- 
340 C. G. S. units. Ans. .9434 ohm. 

5. What length of platinum wire 1 mm. in diameter is required to 
make a one ohm resistance coil? Sp. resistance platinum = 9000 C. G. S. 
units. Ans. 872.8 cms. 

Problems on Heat and Resistance. 

1. Suppose a chain made of alternate links of silver and platinum, 
each .2 mm. thick. What current will keep the platinum red hot, 
500° C? What will be temperature of the silver? 

Specific resistance of silver = 1.634 microhms; of platinum = 9.957 
microhms; radiation per sq. cm. of surface per sec. per degree rise of 
temperature = .001 joule. 

I 9 957 I 

Resist, of platinum link = p x —r.2 = ' in6 X 



TIT 2 — 10 6 ^ 7T (.01) 2 

Joules radiated per sec. = 1QQ0 X 500 X ?r X .02 X Z= "TaTT* ^ 
Joules generated per sec. = (T'R. (2) 

irl it 10 2 



(1) — (2) or C 2 — 10Q X 9957 X j — 9 957 

or C =9956 amperes. 
Joules radiated per sec. in silver = (t — 0) Xj^qq X tt X .02 XI. (1) 

1 fi°-l 7 

Joules generated per sec. in silver = C 2 R = (.9956) 2 X ^ Qs X — rTJTp • 

(1) = (2) or , = ^l^ = 8 2 .05° C. 

2. On a certain circuit on board ship there are 15 lamps each taking 
.7 ampere and a margin of 25$ excess of current is allowed. Find the 
diameter of a lead safety fuse for this circuit. Sp. resist, of lead = 19.85 
microhms, melting point 335° C; loss of heat by radiation and con- 
nection per sq. cm. of surface .001 joule per sec. per degree rise of tem- 
perature. Initial temperature 18° C. 



44 Naval Electricians' Text Book 

Current allowed for = 15 X .7 + 15 * " 7 = 13.125 amperes. 

x, • . - - I 19.85 41 

Resistance of fuse = P x -—* — ~yyr X -^s • 

Joules generated by current per sec. 

= 0»B= (13.125)' X^X^. 
Joules carried away by radiation 

_ (335 — 18) X irdl 



1000 



(1) = (2) or d* = 



(13.125)" X 19.85 X 4 X 1000 
317 X tt 2 X 10 6 




d = .1635 cm. 

3. A potential galvanometer has a resistance of 367 ohms and is 
graduated to show a difference of potential of 100 volts between the 
terminals. Find the diameter of a lead safety fuse which will melt if 
the potential difference rises above 100° C. Temperature of room 20° C, 
other data as in example 7. Ans. d = .01237 cm. 

4. On a circuit there are 65 incandescent lamps in parallel, each lamp 
requiring .6 ampere. If a margin of 30$ excess of current is allowed, 
find the diameter of a lead safety fuse to be inserted in the mains. 
Temperature of room 20° C, other data as in example 7. 

Ans. eZ = .4034 cm. 

5. If a ward room is supplied with 30 lamps, each taking .8 ampere 
and a margin of 20$ is allowed for, what should be the diameter of a 
lead safety fuse to protect this circuit? Temperature of room 18° C, 
other data as in example 7. Ans. d = .2761 cm. 

Temperature Coefficient of a Circuit. 

An electrical circuit is ordinarily made up of resistances com- 
bined in one or more ways and it will be seen later how the different 
resistances of a circuit may be combined in series, in parallel, or in 
a combination of these, and how the value of the resistances may 
be calculated. 

In certain cases the temperature coefficient of parts of a com- 
bined circuit may be required, as when the resistances are made up 
of conductors of different materials. 

Two Resistances in Series. — The case of two conductors of dif- 
ferent materials joined in series is shown in Fig. 2. 



Resistance 



45 



R 1 and R 2 represent the resistances of the two different con- 
ductors joined in series and let a x and a 2 represent the temperature 
coefficients of R t and R 2 . 

The total increase or decrease of R x will be a 1 R 1 per 1° C., while 
that for R 2 will be a 2 R 2 per 1° C, and consequently the resistances 
of each for 1° C. rise will be R, dz a^R x and R, ± a 2 R 2 . 



R, 



R, 



1 2 v v v v. 3 

Fig. 2. — Two Resistances in Series. 



The combined temperature coefficient, which is defined as the 
ratio of the increase or decrease for 1° C. to the original resistance, 
is called a, and 

_ R 1 ± a 1 R 1 + R 2 ± a,R 2 — (R 1 + R 2 ) 



or 



fli + fi. 

, , p " — ohm per ohm per 1 (J. 

1 I -"2 



ft 



If «! is positive and « 2 negative, and a 1 R 1 = a 2 2? 2 a = 0, or the 
total resistance of R x -\-R 2 will be constant at all temperatures, a 
result of great importance in the construction of certain electrical 
measuring instruments. 




Fig. 3. — Two Resistances in Parallel. 



Two Resistances in Parallel. — The case of two conductors of dif- 
ferent material joined in parallel is shown in Fig. 3. 

As before R r and R 2 represent the original resistances of the 
two conductors of different materials joined in parallel and a x 
and a 2 the temperature coefficients of R y and R 2 . 



46 Naval Electricians' Text Book 

It will be shown that the combined resistance of R x and R 2 from 
1 to 2 is 

R X R 2 
R x -f~ R. 2 

The total increase or decrease of R x and R 2 will be a x R x and 
a 2 R 2 per 1° C, and the combined resistance for a change of 1° C. 
will be 

(R x ± ^ t ) (R 2 ± a 2 R 2 ) 
(R x ± a x R x ) + (R 2 ± a 2 R 2 ) 

and the change in resistance due to 1° C. change will be 

(R x ± a x R x ) (R 2 ± a 2 R 2 ) R±R 2 

(R x ± ajtj + (Ro ±aM 2 ) ~~R X + R 2 

and the temperature coefficient for the combined circuit a x will be 

(R x ± a x R x ) (R 2 ± a,R 2 ) R X R, 

„ _ (R x ± aA) + (R 2 ± a 2 R 2 )~R x + R 2 
R X R 2 



R\ "J" -^2 

and this reduces to 

(R x + fl 2 ) (1 ±fl! ±-a 2 -± ffl^a) i , . i n 

a== fl 1 + 3,±a 1 g 1 ±aA -1 ohm per ohm perl C. 

Conductivity. 

Conductivity is the name given to express the ease with which 
substances conduct electricity. A substance of high conductivity 
has low resistance and vice versa, and conductivity is the reciprocal 
of resistance. 

The unit of conductivity is called the mho, and is the reciprocal 
of the ohm. It is the conductivity of a conductor whose resistance 
is one ohm. 

A consideration of the laws of resistance will show that similar 
laws hold for conductivity, and are embraced in the formula 

*-*■ 

The specific conductivity is the conductance between opposite 
faces of a cube, one inch or one centimetre on the side. 



Resistance 47 

Resistance of Series and Parallel Circuits. 

As previously stated, electric circuits consist of conductors of 
various resistances connected in one or more ways to form one or 
more complete paths for the flow of the electric current, and the 
combined or total resistances of the various branches depend on 
the manner in which they are joined. 

There are two main systems of arranging conductors, called 
series system and parallel system, and a complete circuit may be 
of a complete system of either or a combination of both. 

Resistances in Series. — Conductors are joined in series, when 
the end of one is connected to the end of another, all in one line, 
or connected end on to one another, as indicated in Fig. 4. 

R> *< R 3 /x a R 'a a r < 



Fig. 4. — Resistances in Series. 

Any current that flows from A to B must flow through each of 
the several resistances in turn, and the same current must flow 
through them all. The resistance of one is additive to another and 
it is plainly evident that the total resistance of any number of 
separate resistances connected in series is equal to the sum of their 
separate resistances. Thus the resistance from A to B is 
El + R 2 + R 3 + £ 4 + R 5 . 

It is also evident that it matters not in what order the resistances 
are joined, as the addition of each resistance is a positive increase 
to the total resistance. 

Resistances in Parallel. — Resistances are connected in parallel 
when one or more branches of the circuit are connected to the same 
points of the circuit. This is illustrated in Fig. 5. 

Three resistances R x , R 2 , and i? 3 are connected to the same 
points of the circuit, at A and B and it is required to find the com- 
bined resistance of the three, or the resistance of a single conductor 
joining A and B that would allow the same current to flow in the 
circuit to which A and B are connected. 



48 Naval Electricians' Text Book 

The conductance of R t is -~- and similarly for B 2 and B 3 , and it 

1 

is evident that the conductance from A to B is the sum of the 

conductances of the various branches, or the total conductance from 
A to B is 

and as the total conductance is the reciprocal of the total R, 

or 

i2 - R^ R 2 ~^~ R, 
and 

R 1 R 2 R 3 



22 = 



R 1 R 2 -j- R X R 3 -\- R 2 R 2 
If 

ll^ = zv 2 == xv 3 
P /^j i? 2 J? :} 

it: = T ~~ If "" "3 * 




Fig. 5. — Resistances in Parallel. 

As there are now equal paths for the current to now, it is the 
same as though the three resistances had been replaced by one of 
three times the cross-sectional area, and it has been shown that 
resistance varies inversely as the area, so if the area is three times 
as great as one, the resistance would be one-third of each of the 
conductors. 

Resistances in Series and Parallel. — The most common arrange- 
ment of conductors in an electrical circuit is a combination of the 
series and parallel systems as indicated in Fig. 6. 



Resistance 



49 



The resistance from A to B of such a circuit is the sum of all the 
resistances of the several parts, thus from A to B is equal to resist- 
ance from A to C -\- that from C to D -\- that from D to B, and as 
above, total resistance is 



22 = B 1 -f 



■^2-^3 ~T~ -^2^4 I -^3-^4 



+ £= 




Fig. 6. — Combined Series and Parallel Resistances. 



Resistance of Joints and Imperfect Contacts. 

When two dissimilar conductors are joined together either by 
binding screws or soldering, and a current passed from one con- 
ductor to the other, their junction will be either heated or cooled, 
dependent on the direction in which this current is flowing. Con- 
versely, if this junction be either heated or cooled, a current will 
be set up, flowing in a direction dependent on the material of the 
conductors. This heating effect is very small and does not arise 
from any resistance the current meets at the junction of the con- 
ductors. It is simply mentioned in order to distinguish it from 
the resistance that all joints do give rise to, some more than others. 

It is impossible to compute what is the extra resistance added 
to a circuit due to imperfect joints or contacts, the resistance vary- 
ing with the goodness or poorness of contact. It should be seen that 
all joints and connections are perfectly tight, for the less nearly 
perfect they are, the greater the resistance, the more heat developed 
in them and consequently more energy uselessly wasted. Loose 
joints in an electric-light circuit will often cause a fluttering of the 
lights, and many causes mav be sought, when it is only such a little 
thing as a loose connection on the switchboard. 



50 Naval Electricians' Text Book 

One form of a rheostat is composed of carbon blocks, which by 
varying the pressure on them alters the resistance of their contacts 
and so alters the current in the circuit. 

Insulation. 

Insulation is defined as the means adopted for preventing elec- 
tric currents from acting along any other path than through the 
conductors provided for the jrarpose. Insulators are simply sub- 
stances which are poor conductors of electricity, though even the 
best insulator has some conductivity, just as the best conductors 
have some resistance. 

The amount of electricity which insulators allow to pass through 
them is called the leakage, and this takes place through the whole 
cross-section of the insulation, and along the film of moisture on 
the outside surface of the insulation. 

Dirt and moisture act against good insulation, and whenever pos- 
sible insulators should be highly polished to prevent dirt from 
sticking, and they should be coated with some form of non-absorbent 
to prevent the formation of moisture. 

The resistance to leakage is obviously the resistance of the in- 
sulator, and is given by the *same formula as resistance of 
conductors, 

Therefore, the longer the insulator and the smaller the area of 
cross-section, the greater the resistance, or the more efficient the 
insulator. 

Properties of Insulators. — The first requisite of all insulators is 
of necessity high insulation resistance. This should be combined 
with waterproof and fireproof qualities, and with toughness and 
flexibility. For use with high potentials, insulators should have 
sufficient dielectric strength to prevent rupture from sparking. 

Heat affects very materially the insulating properties of sub- 
stances and in some cases it may alter the chemical composition of 
insulating compounds. The insulation of some substances change 
with the degree of electrification, in which cases, heat has a greater 



Resistance 51 

effect. In testing the insulation of electrical conductors the resist- 
ance is not measured until at least a minute has elapsed after the 
conductor is charged. 

Table of Insulators. 



Oils, 


Wool, 


Resin, 


Glass 


Shellac, 


Silks, 


Mica, 


Air. 


Varnish, 


Rubber, 


Paraffin, 




Porcelain, 


Cotton, 


Ebonite, 





Uses of Insulators. 

Rubber. — Some form of rubber, either gutta-percha, India rub- 
ber, pure rubber, or vulcanized rubber is universally ' used as the 
principal insulation for copper conductors. Hard rubber is used 
for washers in the disc or cylindrical form, for switch handles, 
rheostat arms, and the bases of instruments. The ease with which 
it can be pressed or molded into shape makes it particularly useful 
for many purposes. All bushings through bulkheads or beams are 
made of hard rubber. 

Porcelain is used in certain forms of rheostats with the conduc- 
tors imbedded in it, and for the bases on which rest interior fittings 
of wiring appliances. Many washers are made of porcelain or some 
form of earthen ware and used under screw heads or bolts. Porce- 
lain, marble, or slate is used for the foundation of switch-boards 
and panel boards. It is also used for insulators to carry cables 
where conduit or molding is not used. 

Mica is used for the insulation between segments of the com- 
mutator of dynamos and motors, in wiring appliances under the 
fittings, and for covers of fuse boxes. 

This is an excellent insulator; does not deteriorate with high 
temperature and has a high resistance to sparking, and is also 
practically non-hygroscopic. It can be made in thin sheets or built 
up in layers of any desired thickness, and can be made pliable by 
interposing insulating varnish made from shellac or resin between 
sheets. 

Cotton is used in the form of thread on conductors and in the 
piece for insulation of certain parts of armatures, particularly the 
conductors and on the core. 



52 Naval Electricians' Text Book 

Shellac is used where a light insulation is required and in con- 
nection with other insulators. It is rarely used by itself and is 
generally used as an outside covering to prevent the accumulation 
of moisture. Armature laminations are insulated with shellac. 

Paraffin is used to cover the resistance coils in resistance boxes, 
offering at the same time good mechanical protection, as it is put 
on in the liquid state and covers all parts of the coils. 

Glass is used as the dielectric for condensers used in wireless 
telegraphy sets. 

Oils are used for insulation where high potentials are carried. 
The secondary coils of induction coils and certain glass-plate con- 
densers used in wireless telegraphy outfits are often contained in 
receptacles which are filled with oil. 

Different kinds of paper, cardboard, or pressboard are for 
armature insulation. 

Okonite or some form of rubber forms the base of many insu- 
lating tapes and is applied to cotton tape. 

A very good flexible insulation, with fairly high resistance, can 
be made by heating fibrous material with linseed or other oil, drying 
and finally thoroughly baking it. 

Vulcabeston, a mixture of rubber and asbestos, is a very good 
insulator and satisfies most of the requirements. It is unaffected 
by high temperatures, does not absorb moisture, is very hard and 
strong, and has high dielectric strength. 



^ 



CHAPTER III. 

PRIMARY BATTERIES. 

Batteries, defined as combinations of electric cells, are of two 
general classes, primary and secondary or storage batteries. Of 
these two general classes, the former is the only one that has found 
any extensive use on board ship, though even its uses are constantly 
being curtailed by means of current from the dynamos'. They are 
still used for bell work, telephone circuits, for firing guns and 
torpedoes and for exploding electric mines. 

Primary Cells. 

Electric cells all generate electricity by chemical action and the 
term cell is applied to an arrangement in which one or more sub- 
stances forming a fluid or dry mixture act upon two different 
metals, or a metal and carbon placed in the mixture, whereby a 
difference of potential is produced between the metals, a condition 
necessary to the performance of electric work. 

If a piece of metal is placed in a fluid called an electrolyte, there 
is at once produced a difference ■ of electrical condition of such a 
kind that the metal either takes a higher or lower potential than 
the fluid. If two pieces of different metals are placed in the electro- 
lyte, a condition may be produced of one metal assuming a higher 
potential 'than the liquid and the other a lower, in which case if the 
two metals are connected by a conductor outside the liquid, there 
will be a current of electricity established. The current proceeds 
from the metal which has a higher potential than the liquid, or the 
metal which is most actively acted upon chemically by the 
electrolyte. 

Simple contact of dissimilar metals will give rise to a difference 
of potential, and all metals may be arranged in a table so that any 
one element in the list will be electropositive to any one below it; 



54 Naval Electricians' Text Book 

or, in other words, will be of an absolute higher potential than any 
below it when they are placed in contact. One being electro- 
positive to the other means that if a current flows it will be from 
the one which is electropositive to the other. 

Table of Electrochemical Series. 

1. Aluminum, 7. Tin, 13. Platinum, 

2. Manganese, 8- Copper, 14. Carbon, 

3. Zinc, 9. Hydrogen, 15. Chlorine, 

4. Iron, 10. Mercury, 16. Oxygen. 

5. Nickel, 11. Silver, 

6. Lead, 12. Gold, 

In this table the difference of potential caused by the contact of 
any two elements is equal to the sum of the differences of potential 
caused by the contact of all the elements that are between them in 
the list. Thus the difference of potential caused by the contact of 
zinc and lead is equal to the sum of the differences caused by the 
contact of zinc and iron, iron and nickel, and nickel and lead. 

Electrolyte. — The electrolyte must be a substance that will act 
chemically upon at least one of the elements placed in it, and it may 
be either a chemical acid or a chemical salt. The object of the 
electrolyte is to increase the difference of potential between the 
elements placed in it, and by chemical action to keep the differ- 
ence of potential constant, so that when the electric circuit is com- 
pleted, a continuous current may be the result. 

The real source of energy seems to be in the element that is 
acted upon most actively chemically, the other element acting as a 
hand dipping into the liquid to gather and direct the electric 
current. The electric energy is represented by the wasting away 
or the consumption of the element of high potential, and the real 
starting point of the current is at the surface of this element. 

Simple Examples of Electrochemical Action. 

An examination of the table of electrochemical series shows that 
iron is electropositive to copper, so that if these two metals are in 
direct contact, a difference of potential arises causing a current that 



Primary Batteries 55 

will be represented by the wasting away or pitting of the more 
electropositive one, iron. If these two elements are brought in 
contact by salt water, we have all the elements for a simple galvanic 
cell, and the effects of this combination are plainly shown in some 
copper-sheathed ships, the iron near the sheathing becoming pitted 
and eaten away. The same effect is seen in the pittings of copper 
pipes in the salt-water system, the pitting of the copper being due 
to the fact that copper is electropositive to the chlorine in the salt 
water. Where copper pipes come through the side of iron ships, it 
is usual to separate them by zinc rings, so that the zinc-copper 
combination will prevail over the iron-copper combination and the 
zinc will be consumed rather than the iron. These zinc plates may 
be renewed from time to time so as to protect the iron. 

Definitions. 

The following general definitions apply to all single cells : 

The cell is the shell, cup or vessel that contains the elements 
and the exciting fluid. It may be made of glass, porcelain, earthen- 
ware or metal. 

The plates are the elements, metal or carbon pieces that dip into 
the electrolyte, and are generally referred to as the electrodes. 

The electrolyte is the liquid or dry mixture which acts chemically 
on the electrodes. In general it is a liquid that is decomposed by 
a current passing through it. 

The poles are the portions of the electrodes that project from 
the electrolyte. 

The terminals are mechanical devices by which conductors are 
secured to the poles. 

The electrodes are distinguished by one being called positive +, 
the other negative — , the positive one being the one coming first 
in the Table of Electrochemical Series. 

The anode is the positive electrode, the one at which the chemical 
action is the greater and is the plate by which the current enters 
the liquid. 

The kathode is the negative electrode and is the one by which 
the current leaves the liquid. 



1 



56 



Naval Electricians' Text Book 



It should be noted that the positive pole is part of the negative 
plate, and the positive terminal is on the positive pole, while the 
negative pole is part of the positive plate and the negative terminal 
is on the negative pole. 



lu 



-*TT< 
■»P' P- 



C C 



Fig. 



-Typical Primary Cell. 



T= + terminal, 
T' = — terminal, 
P = + pole, 
P' = — pole, 
CC= cell cover, 
(7 = cell, 
E = electrolyte (exciting fluid), 



Zn = zinc strip, 
= + plate, 
= -j- electrode, 
= anode, 

Cm — copper strip, 
== — plate, 
= — electrode, 
= kathode. 



These definitions are illustrated in Fig. 7, showing a simple 
typical cell with its outside conductor. 

The term cell is also applied to the whole combination, the cell, 
electrolyte, electrodes and terminals. 



Primary Batteries 57 



Polarization. 



This is the name given to express the weakening of the current 
when the circuit is closed, due to internal action in the cell, and is 
generally caused by the collection of bubbles of gas on the kathode. 
By the chemical action, which takes place between the electrolyte 
and the anode, gases are liberated from the former and the bubbles 
are carried across the electrolyte and deposited on the kathode. 
All gases offer great resistance to electricity, the result being that 
the current is much weakened, and in some cases polarization almost 
prevents any current from flowing. If the gases are electronegative 
to the kathode, they tend to set up an E. M. E. opposed to the 
original E. M. E. thus still further reducing the current. 

Polarization is gotten rid of in three different ways: (1) by 
mechanical, (2) by chemical, and (3) by electrochemical means; 
the latter preferably by using a second substance separated from 
the electrolyte, or by a solution in the electrolyte which will absorb 
or enter into chemical composition with the liberated gases. 

The depolarizer is the substance used to prevent or counteract 
polarization and may be either a solid or a liquid. 

Local Action. 

This is a name given to the chemical action that goes on in a cell 
when the circuit is open, that is when the outside circuit is broken. 
This is a quiet action and is usually due to impurities in th-3 
electrodes. It ordinarily arises from particles of iron, arsenic or 
other foreign metals in the anode, which in most forms is zinc. 
These impurities being imbedded in the zinc and the zinc and 
impurities in contact with the electrolyte form little closed circuits 
which gradually waste away the zinc. It ,i ; s obviated by using 
chemically pure zinc, but as this is very expensive, by amalgamating 
the zinc, that is by giving it a slight coating of mercury. The 
mercury covers up the impurities and seems to bring only the pure 
zinc to the surface. The amalgamated surface seems to hold a film 
of hydrogen gas which acts to protect it from local action at all 
times. 



58 Naval Electricians' Text Book 

Electromotive Force of Cells. 

As has been stated, the E. M. F. of a cell depends entirely on 
the electrodes and the electrolyte used. In the contact of dis- 
similar metals, the difference of potential is dne alone to the 
elements themselves, and not to their size, shape, or other character- 
istics, and this holds true in an electric cell as far as the E. M. F. 
is concerned, though the resulting current depends very much on 
the size, shape, and distance apart of the electrodes. 

E. M. F. on Open Circuit. — When the circuit is open the differ- 
ence of potential between the poles is always equal to the total 
E. M. F. developed within the cell ; or, in other words, the E. M. F. 
of a cell is the difference of potential between its poles when no 
current is passing through or from it. When the circuit is closed, 
the E. M. F. at the poles is less than the total E. M. F. due to the 
volts lost in driving the current through the internal resistance of 
the cell, and this point must always be borne in mind in connecting 
up cells for any particular work. 

By Ohm's law, the loss of potential in the cell itself is equal to 
the current flowing through the cell multiplied by the internal 
resistance. So if E is the total E. M. F. of a battery due to the 
battery itself, the battery current, and r the internal resistance, 
then the loss of potential or lost volts in the cell is Cr and the 
available difference of potential at the terminals E' = E — Cr. 

To measure directly the total E. M. F. of a battery or cell, it 
must be compared with the E. M. F. of some standard cell, but 
to obtain the E. M. F. of this standard cell, it must be measured 
electrostatically by some means, for in all other ways, there must 
be current drawn from the cell and this will vitiate the result. 

Measurement of E. M. F. — The E. M. F. of a cell may be 
measured directly by means of Sir Wm. Thompson's absolute 
electrometer, which draws no current whatever from the cell. The 
principle of this instrument is that of a condenser with one fixed 
and one movable plate. If these two are connected to two points 
of an electric circuit, between which there exists a difference of 
potential, the movable plate tends to move so as to increase the 
electrostatic capacity of the condenser, and it is moved with a force 



Primary Batteries 



59 



proportional to the square of the difference of potential by which 
the force is produced. The force produced is measured by bal- 
ancing it against known weights. An ordinary condenser with a 
galvanometer and key in circuit may replace the electrometer, when 
comparing the cell with some standard cell. 

There are many laboratory ways of comparing E. M. F., all of 
them requiring some standard cell, or cell whose E. M. F. is accu- 
rately known, certain known resistances and a galvanometer. Gal- 
vanometers are not furnished on board ship, but a very good sub- 
stitute may be found in a double reading voltmeter furnished on 
some ships as a ground detector, and the resistances of the Wheat- 
stone bridge may be used. These will be described later, and 
having these, one method will be described showing how the E. M. 
F. of a cell may be compared with one whose E. M. F. is known. 



£*4= 



© 




=M. 



Fig. 8. — Connections for Comparing E. M. F. of Cells. 



The two batteries or cells to be compared are joined up as shown 
in Fig. 8, their opposite poles being connected by leading wires 
and resistances R and r being inserted in one side of the connec- 
tions, the points A and B being connected by a galvanometer or 
the double reading voltmeter. If the resistance R is fixed, then r 
is adjusted until the voltmeter shows no deflection; or, in other 
words, A and B are at the same potential. When this condition 
holds then 

E x i E 2 '.'. R : t 

from which the E. M. F. of either cell may be found in terms of 
the other. 

The resistances of the leading wires are supposed to be inap- 



60 Naval Electricians' Text Book 

preciable and the resistances of the cells small in comparison with 
R and r, but if not, they must be added to R and r (see Chap- 
ter VI). 

This method is easily arranged and comparison of cells may be 
made in a very short time. For all practical purposes, however, 
the E. M. F. of a cell is sufficiently determined by connecting its 
terminals to the binding posts of a low-reading portable voltmeter. 
The small curent flowing from the cell is inappreciable owing to 
the high resistance of the voltmeter, so that the lost volts in the 
cell are extremely small and the E. M. F. as measured is very near 
the total E. M. F. of the cell. 

Resistance of Cells. 

By the resistance of a cell is meant the resistance it offers to the 
flow of electricity, measured from terminal to terminal, and is the 
sum of the resistances of the separate parts that go to make up the 
internal circuit. It is a physical characteristic depending on the 
elements of which the electrodes are made, of the exciting fluid, 
and of the depolarizing substance, solid or liquid. The resistance 
of the electrodes may be reduced by making them in the form of 
plates, by which a large surface is exposed to the exciting fluid, and 
the resistance of the electrolyte may be reduced by shortening the 
path the current in it has to follow. This is done by bringing the 
electrodes close together, and in some forms, one electrode entirely 
surrounds the other. The resistance of liquids is high as compared 
with metals, and that of gases still higher. The resistance of the 
gases liberated by the chemical action is the chief cause of polariza- 
tion in a cell, increasing the resistance to such an extent that the 
current rapidly falls off. This resistance due to the gases is not 
properly a part of the cell resistance, and being a variable quantity 
is not included in the internal resistance. 

In one method for measuring battery resistance, the battery is 
inserted as the fourth arm in the Wheatstone bridge, and its ordi- 
nary position is taken by leading wires with a key K in circuit. 
The principle and application of the bridge will be shown later, 
it being sufficient at this time to simply state methods and results. 



Primary Batteries 



61 



The resistance a should be as low as possible and b high. With the 
key K open (Fig. 9) current will flow through the galvanometer 
and a deflection of the needle will occur. If on making and break- 
ing the key K, there is no change in the deflection, the points 
where the leading wires are connected to the bridge must have the 
same potential. When this is the case and there is no change in 
the deflection, the following relation holds : 

aR 



B 



R should be 1000 ohms if possible, b 10,000 ohms, and then a will 
usually be less than 20 ohms, b should be adjusted until there is 




Fig. 9. — Connections for Measuring Resistance of a Cell. 

no change in the deflection, but if a change always occurs when the 
key is opened or closed, determine two values of b, one of which 
increases, the other decreases the deflection, and take the value 
which gives the least change. 

The galvanometer should be connected between the junction of 
the two highest and two lowest resistances. 

Note. — For derivation of the above formula, see Chapter VI. 



Resistance of a Working Battery. — When a battery is working 
through an external resistance and a certain current is being drawn 
from it, the internal resistance may and will probably be different 
from its resistance on ' open circuit, and it is frequently of im- 
portance to know what the working resistance is. A sufficiently 
accurate method for determining this is as follows: With a volt- 



62 Naval Electricians' Text Book 

meter (see later) measure the difference of potential between the 
terminals of the battery when on open circuit; call this E x . Make 
the same measurement when working through the external resist- 
ance and call this E 2 , and this should be made before polarization 
sets in. 

When a current is flowing, part of the total E. M. F. is expended 
in sending current through the external resistance and part through 
the battery resistance, but only E 2 , the fall of potential through 
the external circuit can be measured, and E t — E 2 is the fall of 
potential through the battery; therefore, by Ohm's law, where r is 
the internal resistance of the battery, 

(J= E 1 -E, mic = E i> 

or 

If an ammeter (see later) is connected in the circuit, it is not 
necessary that the value of R should be known, as 

E t — E 2 
r- c . 

When two known resistances are available, r can be calculated as 
follows: With the resistance R t in circuit, measure E 2 and C t 
and with R 2 measure E 2 and C 2 , then 

n E<> -. n E 2 

°i- r + ^ i and L *- r J r B 2 

and 

C 1 C 2 

Grouping of Cells. 

Knowing the E. M. F. and internal resistance of the cells with 
which one has' to work, and the character of work to be done, it 
becomes important to know which is the way to group cells in 
order to get the best results. It may be that high E. M. F. is 
desired or a large current, or the greatest current may be wanted, or 
the most economical working may be sought. There are three 



hhl 



H 



Primary Batteries 63 

principal ways of arranging cells, namely, in series, in multiple 
arc or parallel, and in multiple series. 

Series Grouping. — Cells are connected in series when the positive 
electrode of one is connected with the negative electrode of another, 
and the positive one of this to the negative of the next and so on, 
the number so connected being referred to as so many in series. 
This arrangement is shown in Fig. 10. 

The effect of such a grouping is 
to sum up all the electrical and me- ___ 
chanical effects of each cell; that is, 

the total E. M. F. is the sum of the p IG# 10. Cells in Series. 

individual E. M. F's. of each cell, 

and the total resistance is the sum of the internal resistances of each 
cell. If the cells have the same characteristics, then this total E. M. 
F. is the E. M. F. of one multiplied by the number of cells, and the 
total resistance, that of one multiplied by the number of cells. 

By Ohm's law, for a single cell 

L —r+R' 
Where 

C = current in circuit, 
E — E. M. F. of the cell, 
r == internal resistance of the cell, 
R = external resistance in circuit. 

With a number of cells m, connected in series, 

_ mE 
mr -f- R ' 

If there is no external resistance, that is, if the battery terminals 
are short-circuited, R = and 

c _mE _E 
~~ mr — r ' 

or the current is no more than if there was one cell with its termi- 
nals short-circuited. 

If R is very small compared with mr, C = -— , or the current is 

that of a single cell. 



64 



Naval Electricians' Text Book 



If mr is small compared with R, C 



mE 



R 



or in this case the 



h 



h 



h 



h l h 



+ 



current increases with the number of cells. 

Cells connected in series are used on work in which R is already 
large, so that any increase in the internal resistance is not of 
much moment, the increased E. M. F. producing increased current. 
Multiple Grouping. — Cells are grouped in multiple arc, or paral- 
lel, when all the positive electrodes are connected, and all the 
negative electrodes connected, or all the positive electrodes are 
connected to one common conductor and all the negative electrodes 
to another common conductor. This arrangement is shown in 
Fig. 11. 

The effect of this grouping is to practically make one big cell, 

for as was shown under the electro- 
motive force of batteries, the differ- 
ence of potential is due to the elec- 
trodes themselves. In the case of the 
five cells shown, the effect is to make 
two electrodes each five times as 
large as that in a single cell and, 
therefore, the total E. M. F. due to 
these cells grouped in multiple arc is 
the same as that due to one cell. In this arrangement, there are 
now five paths for the current to follow in the battery ; or, in other 
words, the total resistance of these five cells is only one-fifth that of 
each cell. Or, considering two electrodes each five times as large as 
that of a single cell, the resistance of each large electrode would be 
only one-fifth of that of each cell. 

I.f there are n cells connected in multiple arc, and the resistance 

of each is r, the total resistance of the n cells is — , and the total 

n 

current through the battery, neglecting the external resistance 

would be 

n _E__nE 

~~ r ~~ r 

n 

This arrangement, therefore, increases the current, without increase 

of E. M. F. and is used where a strong current is required with low 

E. M. F. or for external work in which the resistance itself is low. 



Fig. 11.— Cells in Parallel. 



Primary Batteries 



65 




Multiple Series Grouping. — Cells are grouped in multiple series 

when some are connected in series, and the groups connected in 
series are grouped in multiple arc, as shown in Fig. 12. 

Here are shown ten cells, groups of two being connected in series 
and five groups of two in 
series being connected in 
multiple arc. The effect of 
this grouping is to give an 
E. M. F. double that of one 
cell, with an internal resist- 
ance of one-fifth of the re- 
sistance of the two cells in 
series, or two-fifths the re- 
sistance of one cell, assum- 
ing they are all alike. 

In general if there are m 
cells connected in series and n groups of m cells each connected 
in multiple arc, the resulting battery current, neglecting external 
resistance would be given by 

G = mB 
mr 
n 
where C, E, and r have the same significance as before. The total 
external current through a given resistance R would be 

mE 



h v h v h v l>-li 



Fig. 12. — Cells in Multiple Series. 



c = 



mr 
n 



R 



It should be noted that the current through each group in series, 

C 
and consequently through each cell, would be — . 

For most battery work, some modification of this system is used, 
depending on the difference of potential and current required. 
It is used also when a higher E. M. F. and stronger current are 
required than any one cell would give. 

Best Arrangement and Efficiency of Batteries. 

a. To find the best arrangement of a given number of cells (N) 
to obtain the maximum current (0) through a given external 
resistance (R) . 



66 Naval Electricians' Text Book 

In addition to the symbols and significations already used, let 
m — the number of cells in series in each group, 
n = the number of series groups in multiple. 
It can be mathematically shown that the current has its greatest 
value when the internal resistance of the battery is equal to the 
external resistance in circuit, that is, when 

m X r 



Total current = 
C = 



R. 

total E. M. F. 
total resistance 

mE 
mr p ' 



Since 

Substituting the value of 
we have 



iV = mX^n = — andm = — 



N . mr -n 



m ! r „ (NR\i, 

and similarly {Nr\z 

This enables us to know how many cells to put in series and how 
many groups to put in parallel to get the greatest current, R and r 
being known. 

b. To find the greatest current which can be obtained from a 

given number of cells (N) through a given external resistance (R). 

As before 

„ mE 



or 





=+*■ 




mr 
n 


-m'x(#,)'x- = * 


C 


~ 2R "" 2 ' 


f N\i 



an equation in which all the quantities are known to solve for G. 



Primary Batteries 67 

c. To find the number of cells in series (m) and number in 
parallel (n) required to give a current (C) through an external 
resistance (R) and to have an efficiency (F). 

By the efficiency of a battery is meant the ratio between the total 
work available in the external circuit and the total work developed 
by the battery. The total work developed by the battery is the 
product of the total E. M. F. and total current (see Joule and 
Watt), and the total available work is the product of the total 
external current and the fall of the potential through that circuit. 

If e = fall of potential through external circuit 

F — efficiency, 

., „ eC e 

then F = EC=E> 



but e = CR and E = C (r + ™) . 



F= * 



R+™ 



or the smaller the internal resistance r, the greater is F. 
From 

F= ^ 

' n 
we have 

mr R(l — F) 
n ~ F > 

and substituting this value in the equation for current we have 

C — mE _rnEF 
~ mr ~ R > 



or 



CR , Cr 

m = -jjrn and n = 



EF ^ <* ~ E(l-F)' 

d. To find the efificiency of a battery arranged (m) in series and 
(n) in parallel through an external resistance (R). 



68 Naval Electricians' Text Book 

There are always two values for the efficiency (F) for any par- 
ticular number of cells (N). 

A7 ^ CR Cr C 2 Rr 



or 



EF * E(l — F) — E 2 F(1 — F) 

F _ E(N)l± (NE 2 — 4C 2 Rr) l 

~ 2E(N)l 



This gives two values for F except when 

NE 2 — ±C 2 Rr. 

Substituting in this the value of N = mn 

, n2 m 2 E 2 F 2 

and C 2 = — o — 

it reduces to 



±F 2 = R X — 
mr 



mr 



Now when R = —^ we have the greatest current, and then 
4F 2 = 1 or F = i or 50 per cent. 

This means that when the cells are so grouped as to cause the 
greatest current, the battery is doing work at its greatest rate, but 
it is only working at an efficiency of 50 per cent, or only 50 per 
cent of the total work is being utilized, the rest being absorbed in 
the battery itself. 

Economical Working. — As far as the cost is concerned the most 
economical grouping would be that which would give the least con- 
sumption of materials, which in most batteries would mean the 
consumption of the zinc, by the consumption of which the chemical 
action is kept up. 

The weight of zinc used is given by the formula w = Czt, where 

w = weight in grammes of zinc consumed, 
C — current in amperes, 

z = electrochemical equivalent of zinc, 

t = time in seconds. 

w is evidently directly dependent on C, so the most economical 
working would be when C is the least, which would virtually be 
the case when the cells are all grouped in series. 



Primary Batteries 69 

Examples of Grouping of Cells. 

1. What arrangement of 24 cells, each of E. M. F. 1.3 volts and resist- 
ance 2 ohms, will send the greatest current through an external resist- 
ance of 13 ohms? 

For greatest current, the internal resistance must be equal to the 
external resistance. 

Let 77i = the number of cells to be grouped in series. 

n = the number of series groups to be placed in parallel. 
m X n = whole number of cells. 



or 



— = internal 
n 


resistance, 


2m —13 


mn = 24. 


n 




m = 12 


n= 2. 



13 = external resistance, 



2. What is the best arrangement to give the greatest current from 
12 cells, E. M. F. of each 1.8 volts and resistance 5 ohms. The external 
resistance consists of an instrument .5 ohm resistance, of the leading 
wires .25 ohm resistance, and two electrolytic cells, one of 4 ohms 
resistance and the other of 3 ohms. Arts. m = 4. 

n = 3. 

3. A battery of 40 cells is to be so arranged that it will send the 
maximum current through an external resistance consisting of two 
branches, connected to the battery by two leading wires, one of resist- 
ance of 2 ohms, the other of 2.5 ohms. One branch has a resistance of 
6% ohms and contains 4 fuses in series, each of 1 ohm resistance, and 
the other has a resistance of 11 ohms and contains 7 fuses in series, 
each of 3 ohms resistance. Ans. m = 10. 

ft = 4. 

4. A circuit is arranged as in the figure. 
The branch a is composed of 10 fuses in series 
and b of 15, each fuse having a resistance of 1 
ohm and requiring .75 ampere to fire it. The 
leading wires have a resistance of 3 ohms. 
How should a battery of 36 cells, each having 
an E. M. F. of 1 volt and resistance .25 ohm 
be arranged to give the maximum current 
through the fuses? Ans. all in series. 

5. Twelve cells, each of which has an E. M. F. of 1.9 volts and resist- 
ance .28 ohm are to be coupled up so as to develop the greatest possible 
amount of heat in a copper wire of .21 ohm resistance. How must 
this be done? Ans. No. of groups in parallel, 4. 

No. in series in each group, 3. 




CHAPTEE IV. 

TYPES OF PRIMARY BATTERIES. 

Batteries for use on board ship are generally confined to one or 
two classes, the Leclanche type being in general use for call, tele- 
phone, and alarm circuits, and some form of dry cell used for firing 
guns, torpedoes, or mines. The use of cells for bell circuits is 
gradually being curtailed by the dynamo current and an illustra- 
tion of how this is accomplished will be given later, but the cells 
in ordinary use will be described. 

Leclanche Cell. 

There are several types of this cell to be found, but their general 
characteristics are the same, differences arising from the manner 
in which the electrodes and depolarizer are made up, this last 
making a difference in the resistance of the various types. 

The positive electrode, or anode, is zinc, as near chemically pure 
as possible, and some forms being amalgamated. This is generally 
in the form of a round strip not unlike a lead pencil in shape. 
The negative electrode, the kathode, is carbon and in different 
types, this is made up in different shapes, and it is this difference 
that makes the various types of this cell. The exciting fluid is 
ordinary clean water in which is dissolved the chemical salt, ammo- 
nium-chloride, or the sal ammoniac of commerce. The depolarizer 
is a paste made of peroxide of manganese, a black powder, mixed 
with powdered graphite. In the earlier forms, the carbon was 
imbedded in this paste which after treatment became hard, and the 
whole filled a porous earthenware cup that stood in the sal ammo- 
niac solution. The porous cup was found to increase the resistance 
of the cell and another form was adopted. In this the depolarizer 
is in the form of hard blocks and these are secured to the carbon 



Types of Primary Batteries 71 

plate, one on each side, by rubber bands, and then the whole is 
placed in the exciting fluid, in which the zinc simply stands. 

In another form of this battery, notably in the Samson and 
Hayden types, the carbon is made in the form of a hollow cylinder 
and the depolarizer is placed inside the cylinder. The cell is an 
ordinary glass jar, coated a short distance from the top with paraf- 
fin to prevent the salts that are formed from " creeping " over the 
top, and covered with a hard rubber top, through which the termi- 
nals of the electrodes project. 

Chemical Action in the Cell. — The action that goes in the cell 
is represented by the following chemical formula: 

aC + b(Mn0 2 ) + c(NH^Cl) + dZn = a C + (b — 2) (Mn0 2 ) + 
(o—2) (NHJOl) + Mn 2 O s + 2NH S + H 2 + ZnCl 2 + (d— l)Zn. 

The current is primarily produced by the action of the ammo- 
nium chloride on the zinc, the zinc gradually wasting away as 
shown in the formula and the salt zinc chloride being formed. 
It is the double salt of this chloride that collects on the electrodes 
and on the sides of the cell and sometimes works its way over the 
edges of the cell. Free ammonia gas is evolved from the ammo- 
nium chloride which escapes or is dissolved in the liquid. Hydro- 
gen is liberated from the ammonium chloride, and this would soon 
cause depolarization were it not for the manganese peroxide. Under 
the chemical action, this salt gradually gives up oxygen and part 
of it is converted into another manganese salt, Mn 2 3 . The oxygen 
thus liberated unites with the hydrogen freed from the ammonium 
chloride, to form water, thus getting rid of the chief cause of 
depolarization. As shown by the formula, the zinc gradually wears 
away while the carbon remains unchanged. 

In one form of this cell, the E. M. F. is about 1.48 volts with 
an internal resistance of 4 ohms, though these values vary in the 
different types. It gives a quick current for a short time, but its 
great advantage lies in the fact that on open circuit it recovers itself 
so quickly. It runs down quickly owing to the formation of the 
hydrogen bubbles, but part of the action goes on when the circuit is 
open, the hydrogen uniting with the oxygen. This quick recovery 



72 Naval Electricians' Text Book 

makes it particularly useful for bell work, where the current is not 
steady or continuous but intermittent. 

With ordinary care a good Leclanche cell should last for years, 
and by this is meant keeping the cells clean, free from accumulation 
of salts on the electrodes, and taking precautions to keep the liquid 
from splashing over as the ship rolls. The battery locker should 
be kept free from dust and be in a cool, dry location. Above all, 
it should be seen that there are no short circuits when the circuit is 
open, as this would soon destroy the usefulness of any cell. 

Sal Ammoniac Solution. — Different classes of cells of the Le- 
clanche type require different strengths of solution to get the best 
results, but an average solution is about five ounces of dry ammo- 
nium chloride (sal ammoniac) to one quart of water. If the 
solution is too strong the double chlorides of zinc and ammonium 
are liable to crystallize and be deposited on the zinc, increasing the 
internal resistance and lowering the E. M. F. 

Effect of Double Chlorides. — There is generally more or less of 
the double chloride of zinc and ammonium present in every sal 
ammoniac cell. This is heavier than the solution of zinc chloride 
and ammonium chloride and sinks to the bottom of the cell. Zinc 
in a zinc chloride solution is positive to zinc in a solution of the 
double salt, the result of which is a local action which tends to 
dissolve the zinc at the top and deposit it at the bottom. The cell 
is practically short-circuited on itself and this explains why almost 
all zincs in this class of cells grow thinner at the top first. Near 
the surface there is a slight oxidation process which also tends to 
thin the zincs. 

Firing Batteries. 

Different forms of batteries are used for firing guns, illuminating 
the night sights of guns, and for firing torpedoes and submarine 
mines. The general form adopted for firing guns and torpedoes 
is a dry cell similar in its electrical conditions to the Leclanche 
type. Some forms used are known commercially as " Roach Stand- 
ard Dry Cell," " 0. K. Cells," " Harrison Electrolyte Jelly Cells." 
The " Dry Cell " is furnished in two sizes, the small dry cell and 
the large dry cell. 



Types of Primary Batteries 73 

In the dry cell, the cell itself forms the anode, being made of 
zinc to which is soldered the terminal. The kathode is a carbon 
slab imbedded in a dry paste which fills the whole cell. Xext the 
zinc cup is a layer of powdered ammonium chloride mixed with 
lime, inside of which is a powdered mixture of graphite and manga- 
nese dioxide in which the carbon is imbedded in the center of the 
cell. .The carbon projects over the top of the cup to which the 
terminal is secured. After the paste is packed in around the 
carbon and fills the cell, the whole is sealed with ]Ditch to prevent the 
access of moisture and for mechanical protection. There is a small 
hole left in the pitch through which a small amount of water may 
be added if necessary and to allow the escape of gases. 

The E. M. F. of the small cell, dry, is 1.5 volts with an internal 
resistance of not over .3 ohm, while the large cell has an E. M. F. 
of 1.5 volts and a resistance of not over .15 ohm. 

For firing, the cells are arranged in firing boxes, there being four 
styles in use, known as " Battery Box Gun Firing," used entirely 
for firing the primers of the guns ; " Battery Box, Combination," 
used both for firing guns and illuminating the night sights ; " Bat- 
tery Box Torpedo Circuit," and " Battery Box, Submerged Tube," 
their names signifying their uses. These boxes are of different 
sizes and shapes, depending on the number of cells to be used, and 
are made of wood, surrounded by galvanized iron, the whole being 
made water-tight by a hinged cover. 

For testing these batteries firing key-boards containing buzzers 
are supplied, the circuit tested by ringing the buzzers before con- 
nected to the firing circuit on the gun or torpedo. In addition a 
small bridge of platinum is furnished which should heat when con- 
nected to the batterv terminals. In firing guns, the circuit is com- 
pleted through the gun, one terminal of the battery being grounded 
to the gun, the other connected to the primer. Two means are 
used for making the circuit, by means of a hand grip which, when 
squeezed, brings contact points together, and by means of a pistol 
grip which closes the circuit by pulling the trigger. For firing 
submerged torpedoes a press key is used. As an additional tester 
for continuitv of circuit a small galvanometer is used. 



74 



Naval Electricians' Text Book 



Common Batteries. 

Although the Leclanche type of cell is used almost to the exclu- 
sion of all others on shipboard, the following table may be useful 
as giving the characteristics of some of the standard common cells : 












STATISTICS OF CELLS. 






Class. 


Name. 


Anode. 


Electrolyte. 


Kathode. 


Depolarizer. 


E.M.F. 


Remarks. 


Mechanical 
depolarizer. 


Volta. 


Zinc. 


Sulphuric 
acid (dilute). 


Copper. 


None. 


.9 


Polarizes 
rapidly. 


Same. 


Smee. 


Zinc. 


Sulphuric 
acid (dilute). 


Platinized 
silver. 


None. 


lto.5 


Same. 


Chemical 
depolarizer. 


Bunsen. 


Zinc. 


Sulphuric 
acid (dilute). 


Carbon. 


Nitric acid. 


1.9 


Kathode 
and depo- 
larizer in 
porous cup. 


Same. 


Grove. 


Zinc. 


Sulphuric 
acid (dilute). 


Platinum. 


Nitric acid. 


1.9 


Same. 


Same. 


Leclanche. 


Zinc. 


Ammonium 
chloride. 


Carbon. 


Peroxide of 
manganese. 


1.48 


High resist- 
ance about 
4 ohms. 


Electro- 
chemical 
depolarizer. 


Daniell. 


Zinc. 


Zinc 
sulphate. 


Copper. 


Copper sul- 
phate with 
crystals. 


LOT 


Kathode 
and depo- 
larizer in 
porous cup. 


Same. 


Chloride of 
mercury. 


Zinc. 


Ammonium 
chloride. 


Carbon. 


Paste of mer- 
curous paste. 


1.45 


Same. For 
small cur- 
rents. 


Same. 


Chloride of 

silver. 


Zinc. 


Ammonium 
chloride. 


Silver. 


Silver chlo- 
ride. 


1.03 


Used for 
testing. 


Same. 


Latimer 

Clark. 


Zinc. 


Paste of mer- 
curous sul- 
phate with 
zinc sulphate. 


Mercury. 


Electrolyte. 


1.442 


Standard 
cell for very 
small cur- 
rents. 



CHAPTEE V. 

SECONDARY BATTERIES. 

Secondary batteries are combinations of secondary cells, or as 
they are sometimes called, accumulators or storage cells. A second- 
ary cell is an electrochemical transformer of energy. In a primary 
cell, the elements are active chemically in themselves and produce 
electrical energy by chemical decomposition, and when the con- 
stituents are entirely decomposed, the cell is dead, and can only be 
made active again by a fresh supply of its constituents. A 
secondary cell can be made active by the passage of a current in the 
opposite direction to that which the cell itself develops. 

Typical Secondary Cell. 

The principle of the secondary cell may be studied by the action 
of a current on lead plates immersed in a solution of dilute sulphu- 
ric acid. Although these lead plates are identical, one may be 
considered positive and the other negative, and the one by which 
the current enters the cell is called the positive plate, or anode, 
and the other the negative plate, or kathode. In its original state, 
such a combination cannot produce an electric current, for whatever 
chemical action takes place between one lead plate and the acid is 
counteracted by the chemical action between the other plate and 
the acid. 

If a current from an outside source is sent through such a combi- 
nation, in a short time oxygen gas is liberated from the water in 
the acid solution and appears on the anode and unites chemically 
with the lead of the plate to form a chemical compound, lead 
peroxide, Pb0 2 . Due to this compound, the anode turns a brown- 
ish color. Hydrogen gas is also liberated from the water in the 
acid solution by the passage of the current and collects on the 
kathode, but no chemical action takes place. The water in the 



76 Naval Electricians' Text Book 

solution which is thus gradually decomposed slowly disappears and 
the solution becomes more strongly acid. 

On stopping the outside current, the cell is now in a different 
electrical condition, and in the place of the two original lead plates, 
there is now one plate of lead peroxide, Pb0 2 , and one of lead, Ph, 
in the electrolyte of sulphuric acid, H 2 SO± . This is now capable 
of acting as a primary cell and generating current by the difference 
of potential existing between the two plates, increased by the 
chemical action which will take place if the plates are connected 
outside the cell. The acid will now act chemically on the plate of 
lead peroxide, and current will result, and in time, both plates will 
become of the same chemical composition and the current will 
cease. This is now a secondary cell and can store up the energy 
given to it until it is required to be used, and can be revived with- 
out using any fresh chemicals, by simply passing a current 
through it. 

Elements of Cells. 

Cells proper can be made of glass, metal, wood lined with glass 
or pitch or celluloid. For stationary work glass is the best, but 
for movable batteries, other forms are chosen. 

The electrolytes used may be alkaline, acid, or neutral, and the 
materials are very numerous, depending on the plates employed. 

The plates may be all metallic, or one set may be of metal and the 
other of carbon, and in some cases neither are metal. 

Plante Cells. 

The earliest reversible cells were those of the Plante type, devel- 
oped by M. Gaston Plante about 1860. They differ only from the 
typical cell described in that the lead plates are made porous, either 
by mechanical or chemical means. Some are cast porous, others 
are built up of lead ribbon, and most of them of different makes 
are treated with nitric acid before being used in the cell. 

The positive and negative plates are identical at the start. They 
have lugs cast on them to project above the level of the electrolyte 
so that the plate may be completely immersed. A strip of lead is 
then soldered to the lugs of those intended to be positives and a 



Secondary Batteries 77 

similar strip to those intended to be negatives for one cell. The 
two sets of plates are then pushed into one another to form a com- 
pact block, positive and negative alternately, each plate being 
insulated from the next one by some non-conductor, as India rubber 
bands, blocks, vulcanite, etc., but remain joined by the lead strips. 
Such a block of plates is held together by rubber bands or a wooden 
frame, and the section, as it is called, is ready to be placed in the 
electrolyte. 

A battery of cells is now formed by connecting the cells in series, 
and the whole is ready for forming. 

This forming consists in sending an electric current through the 
cells for a long time, with the result, that, notwithstanding both 
positive and negative plates start identical in their composition, 
after a time they alter their chemical composition, and soon be- 
come capable of retaining a charge ; that is, a good primary battery 
is obtained with reversible properties. 

- Frequent reversals are necessary to obtain good -capacity and it 
takes a long time before the maximum capacity is reached, and by 
that time the plates become rotten. A reversal is made by com- 
pletely discharging the cells through a resistance, then charge 
again the reverse way, then discharge and again charge, etc. 

Although this type of cell has points . in its favor, such as the 
fact that a large charging current or rapid discharge does not much 
injure the plate, yet it is handicapped by the laborious forming 
process necessan^, and has been superseded by a class of cell known 
as the Faure type. 

Faure Cells. 

In order to increase the output capacity, and to obviate the long 
and costly process of making a cell by Planters method, Faure in 
1880 suggested pasting the lead plates with easily reducible oxides 
of lead. 

Cells of this type are therefore known as pasted cells. The pasted 
plate is made in many ways but the result sought in all is the same; 
that is, to produce a porous leaden or other support carrying paste. 
The paste is carried in holes of different shapes made in the plates, 
which are made of porous lead or an alloy of lead, for strength. 



78 Naval Electricians' Text Book 

The anode or positive plate is usually pasted with a stiff paste of 
red lead, minium (P& 3 4 ), and sulphuric acid, and the kathode or 
negative plate is pasted with a mixture of litharge, lead monoxide 
(PbO), and sulphuric acid. The result of each of these pastes is 
to really form the plates into lead sulphates (PbSO^). After the 
plates are pasted they are allowed to harden, and are then built up 
in sections as previously described. 

The cells are now connected in series and a current passed 
through them for a long time, causing the paste on the positives to 
become converted into lead peroxide, Pb0 2 , and the paste on the 
negatives becomes reduced to finely divided spongy lead. 

During the forming process, the positives become a plum or 
chocolate color, while the negatives obtain a yellowish tint on the 
surface and pale slate color at the edges. 

Chemical Action in Forming. 

The chemical action that takes place in forming is represented 
chemically thus: 
+ plate solution —plate + plate solution —plate 

P0SO4 + H 2 S0 4 + 2H 2 + PbSOt = Pb0 2 + SEJSO^ + Pb. 

lead sulphuric wn t Ar lead lead sulphuric lead 

sulphate acid Wdter sulphate peroxide acid spongy 

The result of the forming is to convert the PbSO^ on the posi- 
tive plates to Pb0 2 , which is thus effected : the #0 4 of each 
sulphate goes to the electrolyte in exchange for oxygen, 0, while 
the hydrogen, H 2 , liberated from the water, H 2 , joins with the 
S0 4 to form sulphuric acid, S" 2 ^0 4 . This is represented as fol- 
lows in the first stage : 

PbSO± + H.80, + 2H 2 + PbSO± = PbO + 3H 2 SO^ + PbO. 

In the next stage, another atom of oxygen, 0, joins the PbO of 
the positive plate, making Pb0 2 , and the liberated hydrogen, H 2 , 
of the H 2 going to the PbO of the negative plate, forming 
Pb + H 2 0, and this second stage is thus represented: 

PbO + 3H 2 S0 4 + PbO = Pb0 2 + 3H 2 80, + Pb. 

The sulphuric acid gradually gets stronger as the forming in- 
creases and its specific gravity consequently increases. 



Secondary Batteries 79 

It will be noticed that the electrolyte, sulphuric acid, H 2 SO^., 
appears to play no part whatever beyond making the water a good 
conductor, yet if it is not added, the chemical actions are not quite 
the same. 

There is an additional action which goes on during forming or 
charging, as gas is given off at all periods of the charge, first off 
the positives only and later off the negatives. This would seem to 
indicate that water is being decomposed, and that the does not 
unite with the paste of the positives and that H is absorbed or goes 
into chemical combination with the negatives, until, when the end 
of the forming approaches, the negatives can absorb no more gas 
and H is given off from these plates. 

Charging of Cells. 

The operation of charging the cells is that of forming as pre- 
viously described, as far as it relates to the chemical action. When 
formed or charged, the positive plate has been changed to lead 
peroxide, Pb0 2 , and the negative to spongy, metallic lead, PbO. 

As charging proceeds, the specific gravity of the acid increases, 
and its conductivity increases, or its resistance diminishes. The 
original solution should be about a 20 per cent solution of pure 
acid; that is, the mixture should contain about four parts of water 
to one of acid, and on fully being charged, the solution will be 
about a 25 per cent solution. Sulphuric acid is a good conductor 
and water a bad conductor, so, on charging, as the acid strength 
increases the resistance decreases. If this were not so, the charg- 
ing current would grow rapidly less as the end of the charge 
approached. 

A well-charged cell has about half the resistance of a discharged 
one, due to the greater conductivity of the electrolyte and to the fact 
that the plates are better conductors when charged. 

It has been stated under the operation of forming that gases are 
given off and the operation is not unlike that of boiling. As the 
surface of the positive plates becomes changed into lead peroxide, 
the material to be acted upon by the current grows less and less, 
and consequently the current is too large to do the work and the 
water of the electrolyte is decomposed. This can be obviated by 



80 Naval Electricians' Text Book 

lowering the current, or stopping it altogether for a time and then 
starting it, when it will be noticed that the boiling does not imme- 
diately recommence. Water should be added from time to time 
to keep the plates well covered, and the specific gravity of the 
acid should be kept up. 

If too large a current is used for the area of the plates, buckling 
is apt to occur, and short circuits in the electrolyte results through 
the plates touching. Buckling is due to unequal expansion of the 
plate and as the paste expands on discharge the expansion and 
contraction should be symmetrical, or the paste is apt to loosen 
from its supports. 

The plates in each cell should be so arranged that the resistance 
from all parts of one plate to every portion of the adjoining one 
should be equal, and if not, buckling is apt to take place. All 
connecting strips should be large and short and the junctions should 
be clean and tight to reduce the resistance. 

Discharging of Cells. 

On the discharge of a cell, the reverse chemical action takes place 
from that on forming or charging. The chemical action is thus 
represented : 

Pb0 2 + 3il 2 £0 4 + PI = PbS0 4 + H 2 SO± + 2H 2 + PbSO^. 

This shows that the cell returns to its original state and in the 
meantime has stored up the energy of the charging current. The 
action also goes on slowly when discharge is not taking place and 
the cell is idle. The gradual loss of charge is somewhat similar 
to the local action that goes on in a primary cell. The lead perox- 
ide and the lead decompose the acid, producing PbSO±, and the 
local action of the positive plate will be more active if there is but 
a thin coating of the peroxide. 

The rate of discharge depends upon the type and size of plate; 
but the discharging current can be larger than the charging current. 
There should always remain about 25 per cent of the total charge 
the cell is capable of taking, and the moment that the E. M. F. 
falls below an average of 1.8 volts per cell, the battery should be 
charged. In testing for this, not the whole E. M. F. should be 



Secondary Batteries 81 

tested, but each single cell should be tested with a low-reading 
voltmeter, which should be carefully calibrated, as a small error 
might make considerable trouble. If in any cell the E. M. F. falls 
to 1.7 volts or below it needs charging, or if the others are up, this 
one should be cut out of circuit. 

When the plates are nearly discharged nearly all the paste on 
the positives is in the form of PbSO^ and this will soon decompose 
into higher sulphates which ruin the plates or cause them to buckle 
when charging. Too rapid a discharge buckles the plates and very 
sudden discharges loosens the paste, even though the current may 
be well within its limit, and current should be drawn slowly from 
the battery until it reaches the maximum desired. Not more than 
25 per cent of the maximum should be suddenly drawn from the 
plates. 

If from any cause, a cell in the battery becomes dead, it should 
be immediately cut out, for on discharging the current will charge 
it the wrong way,- which will reduce the effective E. M. F. of the 
battery by twice its voltage as well as soon ruin the cell, due to the 
formation of sulphates, buckling, and the loss of paste. 

Effect of Specific Gravity of Solution on E. M. F. 

The E. M. F. of a lead sulphuric acid cell varies with the specific 
gravity of the acid of a charged cell, but averages about 2 volts 
per cell. For a variation in voltage for 1.9 to 2.1 volts the specific 
gravity variation is from 1.05 to 1.3, and between these limits, the 
variation of voltage is gradual, but outside the limits the voltage 
varies much more rapidly than the specific gravity. 

Capacity and Output. 

Practically the only limit to the current which a secondary cell 
will give is the resistance to which it is connected, as the internal 
resistance of the cell itself is very low. A short circuit of low 
resistance may produce such a high current that it may burn the 
contacts or even the plates, or produce buckling of the plates. 

The current that can safely be taken from a cell depends on the 
type of cell and the total area of the positive plates, counting both 



8.2 Naval Electricians' Text Book 

sides, and is rated as so many amperes per square foot, and in 
different types and makes may vary from 5 to 25 amperes per 
square foot. 

The capacity of a cell is rated in either ampere hours or watt 
hours, meaning that the cell can be discharged at a certain rate of 
current for so many hours, whose product will equal to the output 
in ampere hours. 

Efficiency. — The efficiency is the ratio of output to input and 

~ ,., „ . ampere hours given out , 

Quantity efficiency = — £ r - — t-. — , and 

17 J ampere hours put m 

^ ^ . watt hours given out 

Energy efficiency = -n— i — r~- — . 

OJ J watt hours put in 

Types of Secondary Cells. 

Many patents have been taken out for secondary cells, but they 
may be generally classified in three classes : 

1. Those in which the active element is formed from the sub- 
stance of the plate itself. 

2. Those in which the active element is formed from some re- 
ducible lead salt applied to the plate. 

3. Those in which one element of class 1 is employed for one 
plate and class 2 for the other. 

Chloride Secondary Cell. — This type of cell presents some pecu- 
liarities in the construction of the plates, chloride of lead being 
used in the manufacture of the negative plates. The chemical 
properties of the positive plate resemble the cells of the Plante 
type, though the mechanical method of construction is different. 
Eor purposes of rigidity, an alloy of lead and antimony is .run into 
molds, and these are so constructed that there are round holes in 
them, closely spaced, each hole tapering from the outside faces 
towards the center. These holes are filled with rosettes of pure 
lead, and they are forced under great pressure into the countersunk 
holes. 

The plates are then formed by coupling them alternately with 
dummy negative plates in sulphuric acid, and passing a current 
through, when all the interstices of the pure lead rosettes are filled 
with a fine coating of lead peroxide, Pb0 2 . 



Secondary Batteries 83 

In the manufacture of the negative plates, pellets of lead chlo- 
ride PbCl 2 are first made, and they aTe assembled on the plate 
molds, which are provided with pins over which the pellets slip. 
Molten lead is then run into the molds under pressure. The cast 
plates containing the pellets of PbCl 2 are then placed alternately 
with zinc plates in a bath containing a solution of ZnCl 2 and short- 
circuited when the following reaction takes place : 

PbCl 2 + Zn + ZnCL_ — 2ZnCl 2 + Pb 

and the pellets become spongy lead. 

When they are connected up with the positive plates with sul- 
phuric acid and charged, the hydrogen evolved combines with the 
last trace of chlorine from the pellets and leaves them pure spongy 
lead. 

The PbCl 2 is formed from mixing known quantities of lead 
oxide, PbO, and acetic acid, C 2 H 4 2 . From this, acetate of lead 
is produced which is treated with hydrochloric acid, HC1, and which 
precipitates all the lead acetate. The solution that is left contains 
acetic acid and lead chloride, according to the reaction, 

Pb(C 2 H s 2 ) 2 + 2HCI = PbCL + 2C 2 H±0 2 . 

The C 2 H 4 Q 2 is separated from the solution by forcing it through 
a filter press while the PbCL is left behind in the form of white 
paste cakes. This is then dried and mixed with a small percentage 
of finely divided metallic zinc and this mixture is heated to a very 
high temperature when it becomes a fluid. This fluid is then 
poured into molds the shape of the pellets. 

Edison Alkaline Cell. — In this cell the positive active material 
consists of a finely divided high oxide of nickel, and the negative 
material of finely divided iron with an electrolyte of a solution of 
potassium hydrate. The active materials are mixed with graphite 
and molded under pressure into thin cakes. The plates are made 
of nickel steel, in which are slots for holding the cakes which are 
also enclosed in thin covering of nickel steel. 

On discharge the iron oxides while the nickel oxide is reduced to 
a lower oxide. 



84 Naval Electricians' Text Book 

Kegulation. 

Since the voltage of a cell may vary from about 1.8 volts at the 
end of discharge to 2.3 volts at the end of charge, a number of 
cells in series will produce a widely varying voltage unless some 
regulating means are provided to compensate for the change of 
voltage. 

The simplest method is to use a resistance in the battery circuit 
but this is objectionable because of the waste of energy. 

A common method consists in varying the number . of cells in 

series. On an E volt circuit, the number of required cells is 

W 

at the time of charging and — - — when fully charged, and an arrange- 

rp jp 

ment must be provided whereby - — - — - — = may be cut out or 

switched in, one by one. These cells are called end cells. The 
terminals of these cells are connected to contact points arranged 
in a circle over which moves a contact arm, which by moving one 
way or the other acts to raise or lower the total voltage by varying 
the number of cells in series. 

In switching from one point to the next, the circuit must not be 
opened, nor must the contact arm touch two adjacent contacts as 
this would short circuit the cell to which these terminals are con- 
nected. The end cell switches are provided with an auxiliary 
contact either on the movable arm or fixed near each main con- 
tact. The main and auxiliary contacts are joined by a resistance, 
and the auxiliary contact rests on one of the switch contacts while 
the main contact touches the adjoining point. By this means the 
circuit is not broken, being completed through the resistance which 
has too low a value to affect the line potential, but is sufficiently 
great to prevent the cell from being short-circuited. 

Series and Parallel Charging. — In the case of most pasted plates 
as received from the manufacturers, the forming process consists of 
a long, continuous charge, lasting over a period from 48 to 60 
hours, and should continue until the specific gravity of the acid 
solution shows no increase for several hours, nor the voltage of any 
cell shows an increase for the same time. The hydrometer is a 



Secondary Batteries 85 

better indication of the state of charge than a voltmeter, though 
both should be used. 

When the plates are first placed in the acid solution the specific 
gravity will fall and a difference of potential of 1.6 to 1.7 volts 
will be given at the terminals of a cell. At the end of the first- 
charge, each cell should show approximately 2.5 volts and the spe- 
cific gravity of the solution should attain its original value. 

The source of charging voltage must be at least slightly greater 
than the voltage of the whole battery, calculated on a basis of 2.5 
volts per cell. Thus, if a battery of 50 cells is to be charged in 
series, a source of at least 50 X 2-5 = 125 volts must be available. 
The smaller the difference between the charging voltage and the 
counter E. M. F. of the battery, the smaller would be the charging 
current, and consequently the longer time it would require to 
charge it. 

If the source of voltage is not sufficient to give the proper charg- 
ing current against the counter E. M. F. of the battery, the battery 
may then be charged in parallel by doubling the charging current. 
Thus, suppose a 110-volt circuit was available to charge 50 cells 
and the desired charging current was 10 amperes ; the 50 cells could 
be divided into two groups of 25 each, making a maximum counter 
E. M. F. of 25 X 2.5 = 62.5 volts. On first starting the charge, 
the counter E. M. F. would be 25 X 1.7 = 12.5 volts, and with a 

10-ampere current, a resistance of ^o — ~ == ^'^ onms w 011 ! - 

have to be inserted in the charging line; the 20 amperes dividing, 
so that each half of the battery would take 10 amperes each. As 
the counter E. M. F. increased, the inserted resistance would have 
to be reduced to keep the charging current constant. After being 
charged in parallel, by a proper arrangement of switches, the bat- 
tery can be discharged in series, and the full potential utilized. 
After charging, the voltage of each cell will fall to a little over 2 
volts on open circuit, and on closed circuit will fall very nearly to 
2 volts. As discharge takes place the specific gravity of the solu- 
tion will fall and on a lower limit, the battery should be recharged. 
If a 220-volt circuit was available, the battery could be charged 

in series, and would require tq = °-^ onms m the ime - 



86 Naval Electricians' Text Book 

Boosters. — If the source of voltage is not sufficiently high to over- 
come the counter E. M. F. of the battery and it is not desired to 
charge in parallel, other means must be used to help the charging 
voltage, and machines for doing this are called boosters. 

An ordinary form of booster for this purpose consists of a shunt 
generator with its voltage regulated by its field regulator. This 
may be run by any means available, preferably by a motor, and so 
arranged in the circuit of the charging source as to add its voltage 
to that of the charging current. By varying the field of this 
booster generator, the charging current can be kept approximately 
constant. 

Faults and Remedies. 

Nearly all the troubles of storage batteries may be traced either 
to buckling of plates or bad forms of sulphating, and these are 
due to want of care either in charging or discharging. Cells that 
are to remain for a long time without use should be thoroughly 
charged, and from time to time, be recharged to keep them to the 
full voltage. This is to prevent the plates from sulphating due to 
local action and slow leakage due to bad insulation. The color of 
the plates will at once indicate sulphating as the positive plates 
instead of being a dark chocolate color will turn grayish all over 
or in patches, and if there is not a marked difference in the color of 
the positive and negative plates, something is wrong. Sulphating 
causes scaling of the plates, falling of the paste, and consequent 
buckling and short-circuiting. 

Bad insulation is a frequent source of leaks, and the shelves on 
which the cells rest should be kept perfectly dry and the glass cells 
should rest on wooden bases supported by insulators. 

If sulphating has occurred, the white patches should be removed 
or else the paste is apt to fall out and they should be scraped off 
and if very bad the sections should be lifted from the cells, taken 
apart and thoroughly cleaned, and the cell itself cleaned of any 
deposit that may have fallen in it. Before removing a section, the 
electrolyte should be drawn off to prevent any danger of short 
circuits. 

Buckling may arise from too high a charging or discharging rate 



Secoxdary Batteries 87 

and often arises from loose paste sticking between plates causing 
unequal resistance and unequal expansion and contraction. Some- 
times plugs of paste fall out and this can happen without being 
noticed, though it usually follows a sudden large discharge. 

The plates should never touch the bottom of the cells and a 
slight quantity of powder is usually found at the bottom, due to the 
white sulphate formed on the first chargings. 

In charging the greatest care must be observed to see that the 
leads of the charging circuit are properly connected, and the 
polarity should always be noted before charging commences. If 
connections are wrong, the plates throughout the battery become 
reversed, and the negatives become brown and the positives slate 
color. There is only one remedy for such a fault, and the cells 
must be discharged through a resistance but not so that the maxi- 
mum discharge is exceeded. When the battery shows no E. M. F. 
or a very low value the leads can be joined up correctly and the 
charging current started very slowly at first, as there is now very 
little counter E. M. F. till the cells are charged up the right way. 
In doing this it is well to vary the current by an adjustable resist- 
ance and gradually allow the current to increase. 

When the plates are sulphated, the internal resistance is greater 
and consequently the E. M. F. is much lower. In charging, if all 
plates are in good condition, they should be charged until they 
boil, but if the capacity of the cell has been reduced by sulphating, 
the boiling will occur too soon. This arises from the charging 
current being too great, as much of the counter E. M. F. has been 
removed. If boiling does not occur at all, the paste may have 
fallen from the plates. 

If a cell gives no E. M. F. from any cause except complete short 
circuit, the discharging current has the effect of charging the cell 
the wrong way. In discharging such a cell it should be discon- 
nected, and connected when charging and in time it may regain its 
original E. M. F. 



CHAPTER VI. 

OHM'S LAW AND ITS APPLICATION TO SIMPLE AND 
DIVIDED CIRCUITS. 

Ohm's law may be stated as follows: The current which flows 
in a circuit is directly proportional to the difference of potential 
between the ends of the circuit, and inversely proportional to the 
resistance of the circuit across which the difference of potential 
is measured. 

In symbols, the law is expressed thus: 

C=§, (1) 

where • C = current in amperes, 

E = difference of potential in volts, 
and B = resistance in ohms. 

From (1) also E = CR, which expression affords a convenient 
way of expressing the law ; that the difference, or fall of potential 
between two points is equal to the current flowing between the tivo 
points, multiplied by the resistance between the two points. 

Problems on Ohm's Law. 

1. An arc lamp requires a current of 8 amperes at a difference of 
potential of 44 volts. What will be the value of an external resistance 
placed in series with the lamp to produce this voltage on a 100 volt 
main? 

The fall of potential through resistance must be 100 — 44 = 56 volts, 
and as 8 amperes flows through this resistance, the resistance must be 

E 56 
R = jy- = -g- = 7 ohms. 

2. An electric heater is connected by means of a cable to constant 
potential mains. When 4 amperes are flowing in the circuit the differ- 
ence of potential across the heater is 98 volts, and when 6.5 amperes 
are flowing, it falls to 93 volts. Find the resistance of the cable. 



Ohm's Law and Its Applicatiox to Circuits 89 

If x = resistance of cable, 4x is the drop of potential in the cable and 
98 + 4x = potential of the mains. 

Similarly 93 + G.ox = potential of the mains, 

or 98+ 4x = 93 + 6.5jt, 

or x = 2 ohms. 

3. A number of 100 volt incandescent lamps are connected at the end 
of a pair of mains connected to a dynamo. If the resistance of each 
main is .37 ohm, and the current is 14.6 amperes, what voltage must 
the dynamo produce at its terminals? 

Resistance of cables = 2 X .37 = .74 ohm. 
Drop in cables = .74 X 14.6 = 10.8 volts. 

Potential at dynamo = 100 +10.8 =110.8 volts. 

4. The resistance of the filament of an incandescent lamp when cold 
is 220 ohms. If this value decreases 35$ when hot, what current will 
a pressure of 110 volts send through the filament? 

5. A resistance of 20 ohms, on being added to a certain circuit caused 
the current flowing to be reduced from 13 to 9 amperes. What was the 
original resistance of the circuit? 

6. An ammeter connected in series with a standard resistance of 
.1 ohm indicates a current of 23 amperes. The difference of potential 
across the standard resistance is found to be 2.28 volts. Determine the 
error in the ammeter reading. 

7. One end (A) of a wire ABC is connected to earth, the other end 
(C) is kept at a constant potential of 100 volts. If the resistance of 
the portion AB is 9.6 ohms and that of BC 2.4 ohms, what current will 
flow along the wire and what will be the potential at the point B1 

Ans. 8% amperes. 
80 volts. 

8. A primary cell, E. M. F. 1.8 volts, and a secondary cell are connected 
up in opposition with a resistance of 400 ohms and the strength of the 
current is observed. On rearranging the cells to send currents in the 
same direction, it is found that the resistance has to be increased to 
4000 ohms in order to reduce the current to its former value. Neglect- 
ing the resistance of the cells, find the E. M. F. of the secondary cell, 
and the current produced. Ans. E. M. F. = 2.2 volts. 

Current =.001 ampere. 

Simple Circuits. 

So far only the difference of potential between two points with the 
relation existing between that difference of potential and the cur- 
rent and resistance have been considered. The next step is to 
consider the total E. M. F. in a circuit and the relation between 
E. M. F. current and resistance. 



90 Naval Electricians' Text Book 

In considering the total E. M. F. Ohm's law may be thus stated : 
The current produced by a source of E. M. F. is dependent directly 
on the E. M. F. and inversely on the resistance. 

In symbols as before 

p E 

where E = total E. M. F. 

This means that the total current flowing through every point in 
a simple circuit depends directly on the total E. M. F. and inversely 
on the total resistance in circuit. The fall of potential around the 
whole circuit is equal to the total E. M. F. or the difference or 
sum of the individual E. M. F's., and is also equal to the sum of 
all the differences of potential from one point to another con- 
tinuously around the circuit. 

By a simple circuit is meant one in which the current follows 
but one path both in its internal and external parts. In other 
words, it is a circuit in which everything that goes to make up the 
circuit is in series with each other. The circuit may be made up 
of cells, leading wires, instruments of different kinds or any electri- 
cal apparatus, provided that everything is connected so that the 
same current traverses every portion of the circuit. 

Fig. 13 represents a typical simple circuit; the battery B com- 
posed of four cells in series, an instrument G, a resistance B x , 
and an electrolytic cell C ± , all in series. The same current will 
traverse every part of this circuit including the connecting wires 
1-2, 3-4, etc. 

If E represents the total E. M. F. of the four cells and C the 
current, r' the resistance of all the connecting and leading wires, 
and r the total internal battery resistance, then 

XT 

C = r + r' + G + B 1 + C 1 9 (a) 

G, B x , and C ± representing the resistances of the parts so lettered. 

The fall of potential from 1 to 2 = C X resistance of 1 — 2 

" 3 to 4 = C X " "3 — 4, etc. 

through C 1 =CX0 1 
" R t =CX 2*i 
G=CXG 
the battery = C X r. 



Ohm's Law axd Its Application to Circuits 



91 



The fall of potential all around the circuit from 1 around again 

t0 * 1S> CV + CC 1 + CE 1 + CG + Or, 

and this must equal E, the total E. M. F. of the battery; this corre- 
sponding to equation (a). 




\\\m 

B 



R. 




Fig. 13. — Simple Typical Circuit. 



Problems as Applied to Simple Circuits. 
1. A circuit consists of a dynamo of .5 ohm resistance and four 
separate resistances of 2, 6, 20, and 1.5 ohms respectively. If the total 
B. M. F. of the dynamo is 120 volts, find the value of the current flowing 
and the drop or fall of potential in each resistance. 
E 120 



v - R ~ 


" .5 + 2 + 6 + 20 + 1.5 






Drop in separate parts = 










4X 2 


= 


8 


volts. 




4X 6 


= 


24 


- 




4X20 


= 


80 


u 




4X 1.5 


= 


6 






4 X .5 


= 


2 


" 



Total drop = total # = 120 volts. 

2. A battery produces a difference of potential at its terminals of 1.8 
volts when sending a current of 2.2 amperes through an external resist- 
ance. Assuming the internal resistance of the battery to be .74 ohm, 
what is the total E. M. F. of the battery? 

The fall of potential through battery, or lost volts 

2.2 X .74 = 1.63 volts. 
Total E. M. F. = 1.8 + 1.63 = 3.43 volts. 



93 Naval Electricians' Text Book 

3. A battery of 20 similar secondary cells sends a current of 6 am- 
peres through the coils of an electromagnet haying a resistance of 4 
ohms. Determine the internal resistance of each cell, assuming each 
to have an E. M. F. of 2 volts. 

C _E__ „_40__ 

6r' = 16 r' = 2.7 

r'each = -^- = .135 ohm, 

or the drop in potential through electromagnet = 6 X 4 = 24 volts. 
.'. drop in battery = 40 — 24 = 16 volts, 

or r' = -g- = 2.7. 

Counter E. M. F. in a Circuit. — If there are one or more sources 
of E. M. F. i,n a circuit, the total is either the sum or the difference 
of the individual E. M. F ? s. Where one E. M. F. acts against the 
source of supply it is said to be a counter E. M. F. and one of the 
best examples of this counter E. M. F. in a circuit is that of a 
battery of secondary cells being charged from a dynamo. The 
E. M. F. of the battery acts against the E. M. F. of the dynamo, and 
current will only flow from the dynamo if its E. M. F. is the greater. 
Having found the E. M. F. required to exactly balance the counter 
E. M. F. of a battery, the additional E. M. F. required to send a 
charging current through the battery may be found by multiplying 
the total resistance of the battery by the current required. 

Problems on Counter E. M. F. 
1. A battery of 50 secondary cells is to be charged from a 125-volt 
mains, the current not to exceed 15 amperes. Assuming each cell to 
have an E. M. F. of 1.8 volts and an internal resistance of .004 ohm; 
determine the value of a resistance that will have to be put in series 
to accomplish the desired result. 

Counter E. M. F. of battery 
Total internal resist. 
Additional E. M. F. to force 15 amperes 

through battery: 
Total E. M. F. required at terminals 
Drop of. potential in resistance 

.'. resistance = ..-v 



= 50 X 
= 50 X 


1.8 

.004 


= 90 volts. 
= .2 ohm. 


= 15 X 

= 90 + 
= 125 — 


.2 
3 
93 


= 3 volts. 
= 93 volts. 
= 32 volts. 


= 2.13 ohms. 





Ohm's Law and Its Application to Circuits 93 

2. Two cells of E. M. F. 1.8 volts and 1.08 respectively are placed in 
a certain circuit in opposition. The current is found to be .4 ampere. 
What current will be produced if the cells are properly placed in series. 

E 1.8 — 1.08 
C = - Jf orA = — g 

# = 1.8 C' = i^-*— 8 =1.6 amperes. 

3. A battery of 50 storage cells is connected up with 5 connected 
the wrong way. Assuming the E. M. P. and internal resistance of each 
cell to be respectively 2 volts and .02 ohm, determine what voltage 
lamps in circuit would get (1) with the faulty connection (2) if they 
were connected up properly. Resistance of leading wires to lamps .2 
ohm and of the lamps 4 ohms. Ans. (1) 68.9 volts. 

(2) 76.9 volts. 

Divided Circuits. 

By a divided circuit is meant one in which the current does not 
follow one continuous path from the source of E. M. F., to its 
return, but rather two or more paths either in its external or 
internal parts, or both. 

In order that the currents in the separate branches that go to 
make up a divided circuit may be calculated, it is necessary to know 
the resistances of the separate continuous branches that make up 
the whole circuit, and it is important to know what the joint 
resistance of two or more branch circuits may be. 

Joint Resistance and Conductivity. 
A 




B 

Fig. 14. — Resistances in Parallel. 

If A and B, Fig. 14, are two conductors joined at a and h, it is 
required to know the joint resistance, or total resistance of A and 
B. These two conductors offer two paths for the flow of current, 
so the sum of the currents in A and B must equal the total current 
flowing from a towards b. 



94 Naval Electricians' Text Book 

Conductivity represents the conducting property of conductors, 
and the joint conductivity from a to ~b, is the sum of the conduc- 
tivities of A and B. The greater the conducting power of a con- 
ductor, the less the resistance must be; or, in other words, the 
resistance is the reciprocal of the conductivity. 
Let 

C A = current in branch A, 

C B = " " " B, 

R A = resistance of branch A, 

R B = « " " B. 

Then the conductivity of A and B = -^ + -^ = i> p B 

±i A K B J^a^b 

and, therefore, the joint resistance of A and B = p „ , 

R A R B 
R A R B 
Ra + Rb 
If there was a third branch C, with resistance E the joint 

resistance would be — = -— = ^-y,- — i, ™ - 



Ra+Rz + Rc 



Ra Rb + RaRq+ Rb Rc * 



If e is the difference of potential between a and ~b, by Ohm's law 

e = C A R A = C B R B , 
or 

G A : C B \: R B : R A , 
and 

Ca + C B : C A : : R A + R B : R B , 
or 

C A = R~-jf 0, where C=C A +C B 

and similar] y C B — n~ — fL p- O. 
K A + JtC B 

By substituting in C A its value from e = C A R A it follows that 

Ra Ra + Ri 

or 



C, 



e __ R A R B q 

R A -t- i? B 



Ohm's Law axd Its Applicatiox to Circuits 



95 



This shows that the fall of potential e from a to b is equal first, 
to the current in one branch multiplied by the resistance of that 
branch, and the same for the other branch, and it is also equal to 
the total current in both branches C, multiplied by the total re- 

7? 7? 

sistance of both branches, p A J r . 

Laws of Divided Circuits — Kirchoff's Laws. 

A consideration of the above facts leads to two laws by which all 
problems connected with divided circuits may be solved. 

a. The algebraic sum of all the currents meeting' in a point is 
zero, that is, the sum of all the currents flowing towards a point is 
equal to the sum of all those flowing away from it. 

b. The total E. M. F. or fall of potential around any one closed 
circuit is equal to the sum of the products of the current from one 
point to another by the resistance of the conductor between the 
same points taken consecutively around the circuit. 




k Df fa la 



Fig. 15. — Illustration of Divided Circuits. 



The application of divided circuits finds continual use in the 
practical arranging of batteries and outside circuits for firing 
primers, torpedoes, and defense mines, and also in calculations for 
determining the different efficiencies of dynamos and motors, all 
of which will be explained later by practical examples. 



96 Naval Electricians' Text Book 



Illustration of Divided Circuits. 

As an illustration of the method used in solving problems in- 
volving divided circuits, the following is given : 

Given a divided circuit as shown in Fig. 15, the resistances being 

marked on the several branches. Given the current in the branch 

ABC as .72 ampere, find the total battery current and the total 

E. M. F. of the battery. 

90 X 10 
Joint resistance of G and D = q A _i_ -in = 9. 

Eesistance of ABC = 9 + .5 +.5 = 10 

« EF and II = 4^|£ = 4 

o + 20 



" AEFC = 4 + 3 + 3 = 10 

" AEFC and K and ABC 

10X20X10 



— 10X^0 + 10X10 + 20X10 
" MABCN = 4+ 1 + 1 = 6 

" MABCN and L = l * l\ — 5.4. 
6 + o4 

Total resistance in circuit = 5.4 -\- .6 = 6. 

Difference of potential between AC = current in ABC X res. ABC 

= .72 X 10 = 7.2 

Current in AEFC = difference of potential between 

AC -T- resistance AEFC = y| = .72 

Current in ARC = difference of potential between 

7 2 
AC -f- resistance AIiC = ^tt = -36. 

Total current flowing in il/A and iY<7 = .72 + .72 + .36 = 1.8. 
Difference of potential between M and N = current in MABCN X re- 
sistance MABCN = 1.8 X 6 = 10.8 
Current in L = difference of potential between 

1 A O 

M and 2V -=- resistance L = -^ = .2. 

Total current flowing in battery = current in MABCN + cur- 
rent in L = 1.8 + .2 = 2 amperes. 
Total difference of potential or E. M. F. = total current X total 
resistance — 2 X 6 = 12 volts. 



Ohm's Law and Its Application to Circuits 



97 



Shunts and Compensating Resistances. 

In making certain electrical measurements it is necessary that 
either all or a fraction of the current in the circuit be conducted 
through the measuring instruments. If currents are large, it is 
frequently not feasible to allow all the current to pass through the 
instruments, partly on account of the mechanical objections but 
generally on account of the delicate construction of the instru- 
ments which would be ruined by excessive current. In such cases, 
it is usual to employ a resistance called a shunt, which is placed 
in parallel with the instrument, and of such a resistance that most 
of the current will pass through it and only a small fraction 



through the instrument. 



(VWVWWN 




Fig. 16. — Illustrating Use of Shunts. 



In Fig. 16 is represented an instrument G in series with an 
electrical circuit AB and shunted by the resistance 8, called the 
shunt. 

This is a case of divided circuits, in which the current in AB 
divides, part flowing through G and part through 8. 

If C = the total current 

C a = current through G 
C s = « " 8, 

then G = C G + C S . 

If G = resistance of the instrument 

S= " " shunt, 

then by the first application of Ohm's law 

C G G = C 8 S, 
and 



.•..C = (-|+l)<7.. 



(1) 



98 Naval Electricians' Text Book 

The factor (-q- +1) is called the multiplier, being the factor 

by which the current in G must be multiplied in order to find the 
total current. 

To find the currents in G and S, we have from (1) 

° G = \&+s) G > 

and it can similarly be shown that 

c s = [g~+~s) g - 

Compensating Resistances. — The addition of a shunt to reduce 
the current flowing through an instrument results in making two 
paths for the current to flow and consequently the resistance is 
decreased and the current increased over its original value. In 
order to reduce the current to the original value, resistances, called 
compensating resistances, are placed in series with the current. 

Problems on Shunts and Compensating Resistances. 

1. A galvanometer having a resistance of 18 ohms is shunted by a 
resistance of 2 ohms. Calculate the value of the multiplying power of 
the shunt, and the compensating resistance. 

J/ =TT + 1 =¥ + 1 = 10 - 

The original current C" = -jg and C = ^g . 

"20 
To reduce C to C" an additional resistance r must be introduced such 
that 

r + 20 
or 

18 = r+ 7>q or r = 16.2 ohms. 

2. A certain galvanometer of 4 ohms resistance requires a current of 
.01 ampere to produce a full scale deflection. Calculate the resistance 
of a shunt which, when used in conjunction with the galvanometer, 
will give a full scale deflection for 100 amperes. What resistance must 
be inserted in series with the galvanometer in order that a full scale 
deflection may be obtained for 100 volts. 

c — 

100 — f-i + 1 1.01 S = .0004 i: 









Ohm's Law and Its Application to Circuits 99 

If the fall of potential through galvanometer is to he 100 volts and 
current ,01 ampere, the resistance is 

tf = -§- = ^ = 10000, 
or 10000 — 4 = 9996 ohms must be added. 

3. A millivolt-meter with 100 scale divisions has a resistance of 1.5 

ohms. Calculate the resistance to be put in series with the instrument 

in order that the full scale deflection shall represent 100 volts; also 

calculate the resistance of a shunt in order that the full scale deflection 

shall represent 10 amperes. 

1 1 

One hundred scale divisions will represent 100 X Jq^q = Jq volt or 

with this voltage and resistance 1.5 ohms, the current through volt- 
meter is 

1 

n 1F 1 

^=T5=15 ampere - 

To represent 100 volts at the terminals, the total resistance must be 

E 100 
R = —g — -y- = 1500 ohms 

and the added resistance 1500 — 1.5 = 1498.5 ohms. 

C = (-°-+l)c orl0 = (^ + l)r 5 - 
.'. £ = .01007 ohm. 

4. When measuring the value of a certain resistance, the volt-meter 
was connected up so as to measure the voltage, not only across the 
resistance, but also across the ammeter. The resistance of the volt- 
meter was 200 ohms, and of the ammeter .005 ohm. The ammeter read- 
ing was 25 amperes, and the volt-meter reading was 4.8 volts. Calculate 
the true value of the resistance. Ans. .187 ohm. 

Problems as Applied to Divided Circuits. 

1. The torpedo circuits (figure 17) A and B, are connected by a 
battery of E. M. F. of 17.5 volts and a total re- 
sistance of 3 ohms. The leading wires C. D, A, 
and B have a resistance of 1 ohm each. In A 
are 4 fuses in series. How many in series in 
B can be inserted, so that all will ignite simul- 
taneously? Each fuse has a resistance of .5 
ohm and requires .5 ampere to ignite it. 

To insure ignition it must be assumed that 
.5 ampere flows in B, for A's resistance being 
less, there will be more than .5 ampere in that 




100 



Naval Electricians' Text Book 



branch, and how much more flows in that branch is a matter of indif- 
ference, as if each branch has .5 ampere or over, the fuses will all 
ignite together. 

x = No. of fuses required, 
C = Current in battery, 
C A = " " branch A, 

C B =- " " " B, 

then 17.5 = 3X0+0X1+ (4 X. 5 + 1) C A + C X 1, 
17.5 = 3X0+0X1+ UX. 5 + 1) .5+0X1, 
C= C a+C £ 0^+.5 = 

15 



17.5 = 5C A + 2.5 -f 30 A or C A = g 



41 



or a? = 4 X-g =20. 



ZG A — (.5a; + 1) .5, 

2. A battery (figure 18) of 15 volts E. M. F. and 6 ohms resistance 
has its poles connected by three circuits in multiple 
arc. Two of these contain fuses and their resist- 
ances with the fuses are 2 and 3 ohms respectively. 
What is the greatest resistance that can be given 
the third circuit without igniting the fuses, if % 
ampere be required to ignite a fuse? 

The current of y% ampere must be in the circuit 
of smallest resistance. Solve as preceding prob- 
lem. Ans. a? = % ohm. 

3. "With a constant E. M. F. of 5 volts at E 
(figure 19), what is the current through h, a, h, 

and c, the resistance of the parts FhG, FaG, FbG, and FcG being 8, 4, 3, 
and 6 ohms respectively? 




Fig. 18. 



Z.JL 



5 = 8C ft + 4C a , 
4C a =3C & = 6C c , 



or 



5 = 80, 



Ci^^-a 



8X4Q a 8X4Q a 

3 + 6 +4C " 

= .238 O c =-| X C a = 

C h = .1785 + .238 + .119 = .5355 




or the total external resistance = — 

% + % + 



C h 



45 
Y2 — y4 = .5356 as before. 



8 + T 

4. A battery of 4 cells is arranged as in the diagram (figure 20). 
Required, the current through the battery and the wire E, and the 
difference of potential between B and O. The E. M. F. of each cell is 






Ohm's Law and Its Application to Circuits 



101 



1.8 volts, resistance of each cell .5 ohm, resistance of AB = 2 ohms, of 
CD = 3 ohms, # = 4 ohms, F = 6 ohms, (? = 7 ohms. 

If the wire G were cut, would the current through the battery be 
increased or decreased; would it be increased or decreased through El 



Total # = 4X.5 + 2 + 3, 



4X6X7 



o=4-= 



+4X6+4X7+6X7 
4 X 1.8 



R — R 
819 ampere through battery, 
30, 

7.2 — 5.733 = 1.467, 



1.467 



= .366. 




If G were cut, the resistance would be increased, 
and the battery current would be decreased. 

Difference of potential between B and (7 = 4(7^ = 1.467. 

4lC e = E — 7(7. Now if C is decreased, 4(7g,is increased and that 
being the difference of potential between B and (7 the current through 
E would be increased. 

5. The interpolar portion of a voltaic circuit consists of three separate 
wires in multiple arc, their resistances being 30, 50, and 70 ohms. If 
the E. M. F. of the battery is 5 volts and internal resistance 6 ohms, 
find the current in battery and through wire of greatest resistance. 

Ans. Battery current .24 ampere. 

Current through greatest resistance .0508 ampere. 

6. Suppose a battery and wires connected as in the diagram, figure 
21. 

Resistance of ABB = 50 ohms, ACB = 30 ohms and EB an unknown 
resistance. A volt-meter connected at E and B shows the same reading 
as when connected at A and (7. The resistance of AG being y 3 of ACB, 
find the resistance of EB. 

30 




e A.C = -g- X &A.C = X X 



50 



unknown resistance 
30 X C AC C=C A1 



+ C A( 



Ceb = -^Cac+ ^ac = -^^a 



10 x C AC _ 
C* 



Fig. 21. 



= X 

10 x C 
or f — 



x = 



AC 



n 
5 X ° AC 



= 6.25 ohms. 



102 Naval Electricians' Text Book 

7. Three parallel circuits contain 14, 10, and 4 torpedoes respectively 
and resistance of leading wires in each circuit is 1 ohm. What is the 
smallest number of cells (E. M. F. of each 1 volt and internal resistance 
of each .6 ohm) required to explode all the torpedoes simultaneously 
and how must the cells be arranged? Resistance of each fuse .5 ohm 
and requires 1 ampere to fire it. 

Assumption neeessary: that the current in the greatest resistance 
must = l ampere. Ans. 96 cells required; 6 groups in parallel, 

and 16 cells in series in each group. 

8. Taking problem 4 under grouping 
of cells, what resistance added to I will 
prevent the firing of the fuses? Find the 
greatest resistance which, used a shunt 
between the poles of the battery, will 
prevent firing (figure 22). 

Solution of the problem mentioned 
shows that the battery should be com- 
posed of 36 cells, all in series. 

If in a there is anything less than % 

FlG 22 ampere, the fuses will not fire in that 

branch, and in & the resistance being 

greater than in a, they will not fire. If there is just % ampere in a, we 

10 
have 10C a = 15C&, or d, = -y^- X % = % ampere, or the whole current 

5 
must be % + % = j ampere. 

The problem now becomes, what resistance R added in series in the 

5 
main circuit will make the battery current = 7- ampere. 

^ , , E total nr . 36 5 

C total = „ . ^. > or 




R total 36 X X A + R + ext. res. — 4 ' 

ext. resist. = 3 + \° * * * = 9 or 5R = 36 X 4 — 90, 

R = 10.8 ohms. 

I ampere must be the least current in the external (fuse) circuit in 
order that the fuses will not fire. 

9x 
Total external resistance = 77—, — , 

9 + x 

9x 5 (9 + x) 

or C X ft 1 M = 9 X fuse current or C total = 



9 + x — " ~ iUO " " Ui * c "" ^ v WM " — ix 

C total ~ ^ t0tal - 36 _ 5Q + *> 
c total _ R tQtal 9x _ ix 



+ 



or 



9 + x 

36 X 4x X (9 + jr) K / Q 1 "^ „ — ** ^ mo 
ST+i^ =5(9 + *) z-7.5 ohms. 



Ohm's Law and Its Application to Circuits 



103 



Illustration of Application of Kirchoff's Laws — Derivation of 
Formula for Comparing E. M. F. of Cells and for 

> Finding Resistance of a Cell. 

(See Chapter III.) 
By Kirchoff's laws, Fig. 23, 




Fig. 23. — Connections for Comparing E. M. P. of Cells. 

C x = C -f~ C 2 , 
E x = C t R x + CG, 

E 2 = C 2 r — CG, 

substituting the value of C x in (1), in (2) 

E x — CR X + CM X + CG, 
from (3) 

CG + E 2 



(1) 
(2) 
(3) 



or 
and 



C 2 

2. r 

E x r = CR x r + CGR X + R,E 2 + CGr 
c= E t r — E 2 R X . 



i^!?- + GZ^ + Gr ' 
when the balance is established C = 0, or 
E x r — E 2 R x = 0, 



or 



# 



£, 



^ 2 " r ' 
If the resistances of the batteries cannot be neglected, they must 
be added to R x and r, or 

E 1 {r + r")=E 2 {R 1 + r'). (4) 

By adding a resistance P to R t and § to r, we have 

£,(»• + r"+<?)=.E' 2 (£ 1 + r' + P). (5) 



104 



Naval Electricians' Text Book 



From (4) and (5) E X Q = E 2 P, 

° r E \ P 

or the E. M. F's. of the two batteries are directly proportional to 
the added resistances after balancing in R x and r. The service 
testing set can be used for the resistance R t and r, the balance 
arms being used for this purpose. 

Derivation of Formula for Finding Resistance of Battery. 

(See Chapter III.) 




Fig. 24. — Connections for Finding Resistance of a Cell. 



In Fig. 24 let E = E. M. F. of cell, 

C — total battery current, 
Cf = current in g, 
C t> = current in a and b. 

When key is open, current flows through the joint resistances 
(a + b) and g, the resistance of which is , -, J? • 

<;=: — * 



R+B + 



(a+b)ff 



or 



(7,4- 

G,= 



a + b+g 

C,g=C n {a+ b) C, + C„ = C 

or C,(a + b + g) = (a + b-)C 



a + b 




E 



X 






Ohm's Law and Its Application to Circuits 



105 



This reduces to 
0,= 



E(a + b) 



{B + B)(a + l) + g(a+b + B + B) 



When the key is closed and A and D are 
at the same potential, current flows as though 
A and D were directly connected, current 
flowing in the divided circuit h and R in 
series with g, and the whole forming a di- 
vided circuit with a. This is shown in 
Fisr. 25. 



(1) 




Fig. 25. 



The resistance of b and R is 
The resistance of ~b, R, and g is 



bR 
b + R 

bR 

b+R 

bR 



+ V- 



The resistance of b, R, g, and a is f yrrR + 9 J a 

bR , — 
F+R + 9 + a ' 



C = 



E 



C 



bR . 

v+n+9+ a 



C,(a + 
G, = — 



n ( T>R -\ 



a 
bR 

b+R + 9 

E 



C 



B + 



bR 



aC 
X 



b + R 



\ . bR 

+ *> a + F+B + 



bR , 

b+R+9+ a 



(2) 



106 Naval Electricians' Text Book 

When the current in the galvanometer is the same, the deflec- 
tion is the same and equation (1) = (2). 
or 

(b + B)a 

BbR + Big + Bba + BRg + BBa + abR + abg + aRg 

a + b 

— aR + aB + bB+bB + ga + gb + gR + gB' 
This reduces to 

aR(aR + bR + gb + gB) = Z>5(a# + &# + #& + ^72), 

or 

a£ = bB, 
or 



CHAPTER VII. 
MAGNETISM AND ELECTROMAGNETISM. 

Magnetism. 

Magnetism is the science that teaches of the properties of mag- 
nets. The name magnet was originally applied to a mineral known 
as magnetite, an oxide of iron of the chemical composition Fe 3 4 , 
which in its native state has the power of attracting iron. It has 
the power of imparting its magnetic properties to pieces of iron 
or steel brought near it, and such pieces of iron or steel are then 
said to be magnetized and are then called magnets. Iron or steel 
may be magnetized in other ways, the principal of which is by means 
of the electric current. 

The Compass. — One of the most common examples of a magnetic 
substance is seen in the ordinary mariner's compass needle, a 
pivotted needle, highly magnetized, which, when at rest and undis- 
turbed by local magnets, takes a position that indicates magnetic 
north and south. The end of the needle that points towards mag- 
netic north is called the nortli-seeking pole, or briefly the north pole 
of the needle, and similarly the other end is called the south pole 
of the needle. 

This needle acts under the influence of some force, inherent in 
the earth and in the space surrounding it which causes it to take 
a certain definite position. The region surrounding the earth and 
near it seems to be under the influence of this force or of varying 
forces, the origin of which lies in different points on the earth's 
surface. These points are called the magnetic poles of the earth, 
one representing the concentration of all the forces exhibiting one 
peculiarity, which may be called positive, and which is known as 
the north magnetic pole of the earth; another, the concentration 
of all the forces of opposite peculiarity which may be distinguished 
by being called negative and which is known as the south magnetic 
pole of the earth. 



108 



Naval Electricians' Text Book 



Eecent investigations seem to indicate that there is only one north 
magnetic pole but one or more south magnetic poles. Emanating 
and radiating from these poles, there may be considered an indefi- 
nite number of lines, the direction of which at any place represent- 
ing the direction of the resulting forces due to the opposite poles 
at that place. These imaginary lines may be considered as form- 




Fig. 26. — Illustrating Earth's Magnetic Force. 



ing closed curves, running through the earth from the south to the 
north pole, and through the space surrounding the earth, from the 
north to the south pole. 

At any place on the earth's surface, the direction of one of these 
imaginary lines would be that which a freely suspended magnetic 
needle would take. 

In Eig. 26, let the circle E represent the cross-section of the earth 
and N the north magnetic pole. A freely suspended magnetic 
needle n, will turn so as to place itself in the direction of the 
magnetic lines at the place of suspension, and its north end will 
point towards the north magnetic pole, and it is urged towards the 
latter with a certain force called the earth's total force, designated 
bv the letter 7. 



Magnetism axd Electromagnetism 109 

This force may be resolved into two forces, one parallel to the 
earth's surface, called 77 and the other vertical to the earth and 
called V. 

If $ = the angle the needle makes with the horizontal 
then H — I cos 

V = I sin 6 






and I = V H 2 + V 2 - 

As the point of suspension of the needle approaches the poles, the 
angle will increase, and when = 90° 

V = I sin 90° = I. 

At the pole then the horizontal force is zero, the vertical force is 
equal to the total force, and the needle points vertically up and 
down. 

AYhen becomes zero, 

H = I cos 0° = I, 

and at that place, the needle is parallel to the earth's surface 
and there is no vertical force. The locus of all the places where 
the earth's vertical force is zero is called the magnetic equator. 

The angle that the needle makes with 'the horizontal at any 
point on the earth's surface is called the Dip. 

Magnetic Field. 

All the space surrounding the earth and which is subject to the 
forces due to the poles is called the earth's magnetic field, and in 
general a magnetic field may be denned as a space in which mag- 
netic action takes place, or a region in which a magnet pole is 
acted on by a force tending to move it in one direction or another. 
Magnetic fields may be produced by the earth, by magnets, by mag- 
netic substances, by electromagnets, or by electric currents. The 
magnetic field of a magnetic substance is similar to that produced 
by the earth, and all magnets may be considered as small imitations 
of the earth, regarded as one huge magnet. For instance, an 
ordinary bar magnet has its poles and its magnetic equator or 
neutral line and its magnetic field surrounding it, represented by a 
number of lines forming curves through the magnet and the space 
surrounding it. 



110 Naval Electricians' Text Book 

The poles of an ordinary bar magnet are close to the ends of the 
magnetic axis ; they are of equal strength and opposite sign. In 
an indefinitely thin bar, uniformly magnetized, the poles are at 
the extremities of the magnet, and at these points the magnetic 
force is greatest. 

In Fig. 27 is shown the magnetic field dne to a bar magnet, in 
which the dotted lines represent the directions in which the forces 
due to the poles at N and 8 act, while the number of lines is a 



v \ \ 1 1 / / / / // />';--u;\\\\\ \ \ / // 

\ \\\ will// / ' / ^-^ X \ \ \ \ \ \ \\\ / / / 



\ \ \ O'-- /;;.'! i ! i i\ 



N \ \ s V ^ ~— -r— " ^' y / ' 



Fig. 27. — Magnetic Field Due to the Bar Magnet. 

measure of the strength of the poles. All the lines pass through 
the central portion of the magnet, the equator, but begin to emerge 
from the sides of the magnet as the poles are approached on either 
side of the equator. Most of the lines pass through the interior of 
the magnet and emerge from the poles, and each line is continuous 
and completes its path in the region outside the magnet. 

Free Magnetism. — Whenever the lines representing the magnetic 
field emanate from a magnetic substance and pass into the space 
surrounding it, the body is said to possess free magnetism, and any 
magnetic substance placed in this region will become magnetic and 
experience a force of attraction or repulsion. 



Magnetism and Electromagnetism 111 

Thus the magnetism of the bar magnet shown is all free and 
capable of producing magnetic induction. 

Unit Magnetic Field. — A Unit Magnetic Field is defined to be 
one of such strength that it will act on a unit magnetic pole placed 
in the field with a force of one dyne. 

A Unit Magnetic Pole is one of such strength that if placed in 
air one centimetre from a similar and equal pole, it will be repelled 
with a force of one dyne. 

Thus, if it is said that the earth's horizontal component of its 
total force is .2 at any place, it is meant that at that place, a unit 
magnetic pole would be acted on with a force of .2 dyne. 

The strength of d magnetic field may also be defined by the num- 
ber of imaginary lines, portions of the closed curves, embraced in 
a given area at right angles to the direction of the lines. The 
intensity of the magnetic field at any point is represented by the 
number of these lines at that point, and a magnetic field has unit 
intensity, or a unit magnetic field exists when it embraces one line, 
in air, per unit of area, that is per square centimetre. 

Laws of Magnetic Force. — 

First Law. — Like magnetic poles repel one another; unlike mag- 
netic poles attract one another. 

Second Law. — The force exerted between two magnetic poles is 
proportional to the product of their strengths and is inversely pro- 
portional to the square of the distance between them. 

Lines of Force Due to a Magnet Pole.- — If the two magnetic poles 
are unit poles and are one centimetre apart, the force exerted be- 
tween them is 

j. mm! lXl ., ! 
/= -&-=— p~ =ldyne. 

From the definition of unit magnetic field, that a unit magnetic 
pole placed there is acted on by a force of one dyne, it fellows 
that unit magnetic field must exist at unit distance from a unit 
pole. The surface of a sphere one centimetre in radius is equal to 
4-7T square centimetres, and as unit field exists one centimetre from 
' unit pole, or has one line of force per square centimetre, it follows 
that from every unit pole there must emanate A-n- lines of force. 



112 Naval Electricians' Text Book 

Magnetic Moment and Intensity of Magnetization. 

If the strength of the poles of a magnet is m and the distance 
between them is I, the moment of the magnet is 

M = m X I 

The external effect of a magnet is the result of a certain condi- 
tion of the metal which extends throughout the length of the bar, 
and any portion cut from the metal will exhibit the same magnetic 
qualities. If the magnetization of the whole magnet is uniform, 
the moment of every portion would be proportional to its volume. 

The moment per unit of volume is called the intensity of mag- 
netization and is denoted by I, or 

ml 

I= ~T 
where V = volume. 

If the cross-section is uniform, the strength of pole is m — Is, 
as V = Is, where s is the area of cross-section. 

Lines of Force and Induction. 

Lines of force are denned as imaginary lines, which by their 
direction show the resultant of the magnetic forces acting at the 
point, and by their number, the magnitude of the force. The direc- 
tion of the lines of force is that in which a free isolated magnetic 
pole would tend to move if placed in the field, the positive direction 
being that in which a positive pole would be repelled by a north 
pole or attracted by a south magnetic pole. These are supposed to 
exist in air, and the number of lines that are embraced in a unit 
area at right angles to the direction of the lines is a measure of the 
intensity of the field at that point. If the earth's horizontal force 
was given as .2, it would mean .2 of unit strength, or that every 
square centimetre embraced .2 of a line of force, but as this is 
impossible, it would have such a strength that would be repre- 
sented by 20 lines of force per square decimetre. 

The strength or intensity of the field is usually denoted by H, 
and is independent of the source which produces the field. H is 
measured by the force which a unit pole would experience if placed 
in that field. Thus, if a pole of strength m is placed in a field of 
strength H, it would be acted on by a force of 

F = mH dynes. 



Magnetism axd Electromagxetism 113 

Besides the lines of force which pass into the air, there are other 
lines which are conceived as only passing through the metal of the 
magnetic substance; these lines representing the intensity of mag- 
netization in the magnet. The strength of pole m being equal to 
Is, and each unit pole having 4?r lines, the total number of lines of 
magnetization in the magnet itself, independent of the lines of force 
in air, is -i-n-Is, or per unit of area, 4w7. 

The resultant of the lines of force and the lines of magnetization 
are called Lines of Induction. 

Magnetic Induction. 

Magnetic induction is the phenomenon of inducing magnetism 
in a magnetic substance by the influence of another magnet, and a 
magnetic material placed in a magnetic field becomes magnetic by 
the influence of the lines of induction described above. 

Soft iron lying in the magnetic field of the earth becomes mag- 
netic, and of greater or less strength, depending on its position 
relative to the lines of induction of the earth's magnetism. Thus, 
a long, straight bar lying parallel to the lines of force or in the 
magnetic meridian may become strongly magnetic, the part point- 
ing to the north of opposite polarity to that of the north magnetic 
pole of the earth. In this position it embraces a great many lines 
of force. As the bar is turned from the meridian, the number of 
lines embraced continually diminishes and the resulting induction 
grows less, until the bar is east and west, when its ends show practi- 
cally no magnetism. However, in this position, the whole half of 
the bar lying broadside to north will have magnetism opposite to 
that of the north magnetic pole and opposite to the other, half. 

If the bar is held vertical, it will have induced in it, however it 
may be turned in azimuth, magnetism due to the vertical component 
of the earth's total force, the lower end having magnetism opposite 
to the magnetic pole of the hemisphere in which the experiment is 
made. 

Magnetic induction takes place in any magnetic substance which 
is near enough to allow the lines of force from the magnetizing 
substance to pass through it. North and south polarity is always 
set up, and the induced polarity can always be told, if the direction 



114 Naval Electricians' Text Book 

of the inducing field is known, for no matter what the shape of the 
magnetic substance, a south pole will always be formed where the 
lines of force enter the substance and a north pole where they leave 
it. In other words, poles of the inducing substance induce oppo- 
site polarity to themselves, and the pole nearer to the inducing 
magnet will be of the opposite kind. 

A substance magnetized by induction exhibits all the properties 
of a magnet while under the influence of induction, but generally 
loses most of them when the magnetizing substance is removed. 
If the number of lines passing through the material placed in a 
magnetic field is greater than the number of lines that previously 
passed through the same space in air, the material is said to be 
paramagnetic, and if less than before, diamagnetic. Thus, the iron 
bar lying in the magnetic meridian was paramagnetic; if the rod 
had been zinc, the number of lines passing through the zinc would 
have been less than through the same space in air, and it would 
have been diamagnetic. 

Paramagnetic and Diamagnetic Substances. 

A list of some of the principal paramagnetic and diamagnetic 
substances is given : 

Paramagnetic. 
Iron, Nickel, Cobalt, Aluminum. 

Diamagnetic. 
Bismuth, Air, Silver, Water, 

Antimony, Mercury, Copper, Alcohol. 

Zinc, Lead, Gold, 

When a material is lying in a magnetic field the total number 
of lines passing through the material per square centimetre of cross- 
section at right angles to the lines is a measure of the magnetic 
induction and is usually denoted by B. This B consists of the 4tt7 
lines mentioned above as representing the intensity of magnetiza- 
tion per unit area of cross-section and the H lines due to the 
magnetizing force, or B = 4ttZ + H, 



Magnetism axd Electromagxetism 115 

Magnetic Permeability and Susceptibility. 

Suppose a magnetic field of strength H, and a magnetic material 
placed in it experiences an induction B; or, in other words, there 
are B lines per unit of area in the material, while in the same space 

in the air there were but H lines, then the ratio -jt is called the 
permeability of that material, usually denoted by fx, which is called 
the coefficient of permeability. Similarly, if the intensity of mag- 
netization becomes /, the ratio -jj is called the susceptibility of that 
material, denoted by h, called the coefficient of susceptibility. 

7? T 

li. = -jj and k = 27-and F> = 47r/ -f- H, 

whence it follows that /x = kirk + 1. 

Electromagnetism. 

Electromagnetism treats of the relation existing between electric 
currents and magnetic fields. 

Magnetic Field Due to Current in a Straight Conductor. 

If a straight conductor is held oyer and parallel to a small 
piyotted magnetic needle which is pointing towards magnetic north, 
and an electric current is passed through the conductor, the needle 
will be deflected one wa} r or another out of the magnetic meridian. 
This experiment shows that there must have been some force 
brought into existence by the current in the conductor that was not 
present when the current did not flow. 

This deflection of the magnetic needle is not due directly to the 
electric current, as the conductor does not touch the needle in any 
way, but it is due to a condition established by the current, the 
setting up of a magnetic field around the conductor, and it is the 
reaction of the two magnetic fields, that due to the magnet and 
that due to the current, which causes the needle to take a position 
dependent on the resultant of the two forces. 

A straight conductor carrying a current has then set up around 
it a magnetic field which is dependent for its intensity and on the 



116 Naval Electricians' Text Book 

distance its properties are manifested directly on the strength of 
the current. This magnetic field consists of a series of concentric 
curves, or rings, surrounding the conductor, the lines representing 
the field being in every way similar to the lines of force of magnetic 
substances. These lines have no absolute geometrical form, but 
rather are a mass of whirls or eddies surrounding the conductor. 
They are brought into existence by the current, and increase with 
the current and die out with it, seeming to collapse like rubber 
bands that have been stretched, when the current has faded to zero, 
and spreading out as the current is increased. An idea is given of 
their form and direction in Fig. 28. 

In Fig. 28, the lines of force are drawn as concentric circles 
around the conductor, but as a matter of fact as stated above they 




Fig. 28. — Magnetic Field due to Straight Current. 

may or may not have a symmetrical form. In the right hand 
sketch, the central dot represents the conductor, with the current 
flowing away from the observer, in which case the positive direction 
of the lines of force is clockwise or right-handed and the heavy 
circle has been drawn to represent the resultant of all the lines of 
force due to the current. This field will remain of constant in- 
tensity as long as the current remains steady, but will change in 
strength as the current starts, stops, or changes its rate of flow. 

Knowing now the character of the field set up around a con- 
ductor carrying a current and the field of the magnetic needle, it is 
easy to account for the deflection of the needle under the influence 
of a current of electricity. 

The upper figure in Fig. 29 represents the cross-section of the 
conductor flowing away from the observer and marked IN, and the 
circle represents the resultant of the lines of force. Under the 
conductor and parallel to it is shown the cross-section of the needle, 



Magnetism axd Electromagxetism 



117 





Fig. 29. 



the north end marked N. The positive direction of the magnetic 
whirls is clockwise, and these whirls apparently strik- 
ing the north end of the needle, there is a reaction 
between the two magnetic fields, and both being posi- 
tive, there is mutual repulsion, the field of the current 
being pushed out of its natural path, and the north 
end of the needle being repelled to the left. There is 
also attraction between the field of the current and 
the south pole of the needle, tending still more to 
deflect the north end of the needle to the left. If 
the needle were placed over the current, the north 
pole would be pushed to the right and opposite de- 
flection would be the result. 

The resultant action of the two fields is also ex- 
plained by the following general principle: When- 
ever two different magnetic fields are near one 
another and capable of influencing one another, and 
one is fixed while the other is movable, the movable 
one will always tend to move to such a position that will cause the 
two fields to have one common path in one direction. 

In the above illustration, in order that the two fields may have 
one common path in one direction, the needle will have to turn at 
right angles to the conductor, when the magnetic lines due to the 
current would run through the needle from the south pole to the 
north, and from the north pole of the needle around the conductor 
in air to the south pole of the needle. 

Rules for Remembering Direction of Field and Current. — 
The lower sketch shows the conductor over the needle and flow- 
ing up, the needle being deflected to the left. There are several 
rules for remembering the relation between* the direction of the 
current and the directior of ihe deflection of the needle, one being 
the application of the word snow, illustrated in the above sketch. 
If the current is from sou + h to north over the needle, the deflection 
of the north end of the needle is to the west, the initials of south, 
north, over, icest, forming the word snow. 

Conversely by knowing the direction of deflection, and the posi- 
tion of the needle in reference to the conductor, the direction of 
the current is at once known. 



118 



Naval Electricians' Text Book 



One of the simplest rules for remembering the direction of the 
lines of force due to a current is that known as the Hand Rule. 
Grasp the conductor with the right hand with the thumb turned 
away from the hand and pointing in the direction in which the cur- 
rent is flowing. The direction in which the finger tips point is 
then the positive direction of the lines of force. 



Laws of Parallel Currents. 

These laws may be stated here as they are so readily explained 
by a consideration of the magnetic fields surrounding conductors 
carrying currents, and illustrate so well the resultant action of 
those fields. 




Fig. 30. — Magnetic Field of Parallel Conductors in Same Direction. 

Parallel conductors carrying currents of electricity are mutually 
attracted if the current is flowing in each in the same direction, 
and are mutually repelled if the currents are flowing in opposite 
directions. 

Fig. 30 shows two parallel conductors A and B, the current in 
each flowing away from the observer, and each surrounded by its 
own magnetic field, which is indicated by a few representative 
lines. The arrows show the positive direction of the lines of force, 
the same in both cases, each being right-handed or clockwise as 
viewed in the direction the current is flowing. The lines near the 
conductors are closed on themselves, but where they meet, they 
seem to absorb one another and each takes the path and continues 
the course of the other, which is the resultant path due to the 



Magnetism and Electromagxetism 



119 



forces exerted by the separate fields. In the region between the 
conductors, it is seen that though the positive direction of the lines 
of force is in the same direction, at this point they are opposite, 
and each path by itself represents the direction a free north pole 
would move. Here then is like magnetism, and by the principle of 
resolution of forces, it is seen that the resultant will be something 
similar to the curves above. 

In this illustration is seen the analogy of the lines of force to 
stretched rubber bands, there being a tension along the lines tend- 
ing to draw the conductors together. The lines could be imagined 
to be replaced by one line joining A and B such that if all resist- 
ance to motion was overcome the conductors would be drawn 
together. 




Fig. 31. — Magnetic Field of Parallel Conductors in Opposite Directions. 



Fig. 31 shows two parallel conductors A and B, the current 
in A flowing away from the observer with its right-handed or 
clockwise field as viewed in the direction the current is flowing, 
and the current in B flowing towards the observer with its left- 
handed or anti-clockwise field as viewed in the direction opposite 
to that in which the current is flowing. 

By the resolution of forces, it is seen that there is mutual repul- 
sion between the fields in the region between the conductors, each 
field being compressed on its own conductor. The action of the 
two fields is such that there is compression across the lines of force 
while yet tension in the direction of their length. 

As in the above case, the fields could be imagined to be replaced 
by a band in a state of compression which would cause the con- 






120 



Naval Electricians' Text Book 



ductors to be pushed apart if the resistance to compression was 
overcome. 

The resolution of the forces acting in the two cases is shown by 



the following sketch : 




Fig. 32. — Resolution of Forces Due to Magnetic Field. 



In Fig. 32 one line of force is taken to represent the field of A, 
and the north pole travelling in this line at a given instant is 
travelling in the direction* represented by arrow 1, tangent to the 
circle of the line of force. At a similar instant, a free pole in the 
field of B is moving in the direction of arrow 2, both being clock- 
wise. The resultant of these two forces is arrow 3, which is in a 
direction parallel to AB, or the line described by a pole tends to 
embrace both conductors, giving the resultant line as seen in the 
preceding figure of attraction. 

If, on the other hand, the field of B is opposite to that of A, at 
the instant a free pole in the field of A is moving in the direction 
of arrow 1, one in the field of B is moving in the direction of 
arrow 4, the resultant of which is arrow 5, which is in a direction 
perpendicular to AB, or a force which tends to separate the fields, 
causing a compression and a corresponding repulsion of the con- 
ductors carrying the currents. 

If the conductors are not parallel, the reaction of the two fields 
will tend to bring them parallel and in such a parallelism that will 
tend to make both the currents flow in the same direction. 



Magnetism axd Electromagnetism 121 

In the left-hand diagram of Fig. 33, the fields due to the two 
currents would tend to cause the upper and lower halves of each 
conductor to approach one another so that the two conductors would 
he parallel and both currents flowing down. In the right-hand 
diagram, the right and left halves of each conductor would tend to 
approach each other, so as to make the conductors parallel, with 
the current flowing from right to left. 





Fig. 33. — Oblique Currents. 

Magnetic Field Due to Current in a Coiled Conductor. 

Having seen how the magnetic field is produced by a current 
flowing in a straight conductor, we are now in a position to take 
up the field produced by a current flowing in a conductor bent into 
a ring or spiral. In this case the magnetic field still surrounds 
the conductor as a series of whirls of lines of force, at any position 
the plane of the lines being normal to the conductor. Bending 
the conductor into a ring has the effect of increasing the intensity 
of the field in the center of the ring, or region near it, as it con- 
centrates the lines of force at that point. 

Figs. 34 and 35 represent a conductor carrying a current bent 
into a circle, one turn being made. Fig. 34 shows the current in 
the conductor flowing in a clockwise direction, and the lines radiat- 
ing from the center show the projections of the magnetic lines sur- 
rounding the conductor, the positive direction, according to previous 
laws, being towards the center in the half of the circle that is nearer 
the eye. The magnetic lines are only those due to the ring of the 
conductor, not the straight portions of the conductor. 

Fig. 35 shows a section of the conductor on the line AB, and 
revolved to the right 90°. The lines of force 1 and 2 are projected 



122 



Naval Electricians' Text Book 



as circles, 3 and 4 as a straight line and any intermediate lines as 
ovals. These latter are left ont for the sake of clearness. The 
cross in the npper little circle © represents the tail of the arrow 
showing the direction of the current in the conductor, and the dot 
in the lower little circle O represents the head of the arrow. 
Eemembering these directions, it is seen that the upper line of 
force has its positive direction in a clockwise direction and the 
lower in an anti-clockwise direction as shown by the arrows, and the 
inner portion of the center line is in the same direction. 

A 





Figs. 34 and 35. — Magnetic Field Due to Coiled Conductor. 



Eemembering that the positive direction of these lines is the 
direction a free north pole would move, it is evident in the center 
it would move to the left, all the lines of force urging it in that 
direction. From the first law of magnetism, magnets of unlike 
polarity attract, and of the like polarity repel. As this free north 
pole would move to the left away from the left-hand side of the 
conductor, it is evident that that side must act as north polarity. 
Viewed from the right the current is flowing clockwise, which gives 
the rule: If a spiral conductor carrying a current he viewed end 
on, and the current is flowing in a clockwise direction, then the 
nearer face is of south-seeking polarity and the further of north- 
seeking polarity. 

The right-hand face of the right-hand figure acts then as though 
it were a magnetic shell of south-seeking polarity and the opposite 



Magnetism axd Electromagnetism 



123 



face of north-seeking polarity. In the left-hand figure, the plane 
of the conductor nearer the eye is of south-seeking polarity and 
the farther side is of north-seeking polarity. 




Fig. 36.— Two Core Polarity. 

The rule given for determining the condition of polarity holds 
good for either a right-handed or left-handed spiral, as indicated in 
Fig. 36, showing opposite polarity produced in two cores by a single 
winding. 



N 




Fig. 37.— The Solenoid. 



The Solenoid. 

Fig. 37 represents the resultant magnetic field due to a conductor 
carrying a current, the conductor being bent into a number of 
turns, forming a spiral. The field is exactly similar to the case 
of one turn with the exception that the spiral forming the path is 
much longer, with the result that the field in the interior along 
the length of the spiral is almost uniform. Of course, if the con- 
ductor is bare, the turns must not touch in forming the spiral, but 
it is immaterial if the conductor is properly insulated. 

Such a spiral is called a solenoid, and it acts exactly as an air 
magnet, reasoning as above showing the left-hand face to be of 



124 Naval Electricians' Text Book 

north polarity and the right-hand face of south polarity. The 
intensity of the field in the interior is greatest at the center, gradu- 
ally weakening towards the conductor. Only lines of force in the 
center are shown, but these are not the only lines, others being 
parallel to the center line in the interior and close to the inside of 
the conductor. At the ends, the lines of force spread out, the field 
weakening as the distance from the ends increases. 

Magnetizing Force Due to a Solenoid. — It has been shown that 
a magnet of strength m placed in a magnetic field of intensity H 
is acted on by a force of 

F = mil dynes. 

If the pole is of unit strength and moved through a distance I the 
w r ork done, expressed in ergs, is 

Fl = III (1) 

The work done in moving a conductor carrying a current through 
a magnetic field is equal to the current times the number of lines 
cut, or 

Work done = -— ergs. (2) 

C is divided by 10 in order to reduce the number of amperes of 
current to the number of absolute units, as the work done is ex- 
pressed in ergs. 

From each unit pole there radiate 4:tt lines of force and each of 
these lines will cut each turn of the wire around the solenoid, as 
the unit pole is moved against the magnetic force. If there are S 
turns in the solenoid, the total number of lines cut is 

N = 4tt£, 
and the total work done is 

Work done = T Q ergs. (3) 

If the length of the solenoid is I, that is, the length occupied by 
the winding, the work done against the magnetic force, is, according 
to equation (1) = HI, and therefore (1) = (3), or 

TT _ 4ttCS 

H -~ToT' 

This is an expression for the intensity of field within a solenoid 
due to a current flowing in it, and is also the magnetizing force of 
the solenoid. 



Magnetism axd Electron agxetism 125 

Open and Closed Magnetic Circuits. 

A closed magnetic circuit is one in which the lines of force due 
to the magnet flow around a complete iron path; an open magnetic 
circuit is one in which the paths of the lines of force are broken 
by one or more air gaps. The open circuit exhibits free magnetism 
and produces and can induce definite polarity and is sometimes 
called a polar circuit, while the closed circuit possesses practically 
no free magnetism and produces induction in neighboring magnetic 
substances only by the leakage of magnetic lines from it. 

The ordinary bar magnet and the solenoid are examples of open 
magnetic circuits, and forms of open circuits are extensively used 
with continuous currents while closed circuits find their greatest 
uses in alternating currents. 

The Electromagnet. 

When no current is flowing through the conductor forming the 
solenoid, there is no magnetizing force to produce a magnetic field, 
either in the space surrounding the solenoid or in the column of air 
enclosed by the solenoid. When current flows, producing a mag- 
netizing force, the column of air inside is subjected to a magnetiz- 
ing force, producing a field of intensity H, and also an induction B. 

7? 

The coefficient of permeability /x =-^ , of air = 1, as the induction 

£1 

B by definition is equal to H for the substance, air. 

If, however, the conductor forming the solenoid is not wound 
around a column of air, but around a substance of high perme- 
ability, as soft iron, the number of lines of induction B that now 
thread through the iron is very much increased, and the intensity 
of magnetization of the iron is fx times the intensity of the air field 
II. Suppose there were 50 lines of force per unit of area in the air 
column, and the coefficient of permeability was 300, then there 
would be 15,000 lines per unit of area in the iron core. 

Such an arrangement of solenoid and soft iron core is termed 
an electromagnet, the iron core exhibiting the properties of a 
magnet to its fullest extent only when current is flowing. 

An electromagnet is a contrivance intended to exert a force of 
attraction on a movable piece of iron called the armature. Polarity 



126 



Naval Electricians' Text Book 



is induced in this armature by the magnetic field of the electro- 
magnet, after which attraction takes place, the armature being 
made movable so it can approach the core of the electromagnet. 
Before induction can take place, there must be free magnetism, so 
the primary condition is that the magnetic circuit must be an 
open one. 

The design of electromagnets depends on the character of work 
they are expected to do, whether they are to be slow or quick-acting , 
and whether the range of motion of the armature is to be short 
or long. 

Examples of Electromagnets. — A very common and typical form 
of electromagnet is shown in Fig. 38. 



imjiiliiiiiii 



PTMTM 



Fig. 38.— Typical Double-Coil 
Electromagnet. 



n 










ill 


JU in hub a 








j 

! 

i 
i 






IE 


llmrj:: 


mi 




i i v ' ' 



Fig. 39.— Club-Foot 
Electromagnet. 



This consists of two coils of fine wire, C, wound oppositely 
on two bobbins which are slipped over the iron cores, B, which are 
secured to the base of magnetic material, Y, called the yoke. When 
current is sent through the coils, poles of opposite polarity are 
produced in the ends of the cores, B, the open magnetic circuit 
being through the two cores and the yoke. Above the upper ends 
of the cores is secured the armature, A, of soft iron, and so 
pivoted that it can approach the cores. It is made large enough 
to project slightly over the whole area of the cores which are usually 
circular. The free poles in the ends of the cores induce opposite 
polarity in the ends of the armature, after which attraction takes 
place and the armature moves towards the cores and brings up 
against them, forming a closed magnetic circuit. The armature 
will remain attracted as long as current flows, but when it is broken, 
the magnetic field is dissipated and the armature is usually provided 



Magnetism axd Electromagxetism 



127 



with some arrangement by which it is returned to its original 
position. 

This form of electromagnet is very common and is used largely 
in vibrating bells, relays, and like appliances. 

Fig. 39 shows a one-coil electromagnet, known as a club-foot 
electromagnet. 

This differs from the two-coil electromagnet in that it only has 
one coil, the magnetic circuit being completed through the other 
core which is unwound, and which has the same polarity as the lower 
end of the wound core and the yoke. Its action is the same as the 
two-coil type. 

This saves the winding of one magnet but diminishes the pull on 

the armature. . 

A . 

i 




Fig. 40.— One-Coil 
Electromagnet. 





Fig. 41. — Iron-Clad 
Electromagnet. 



Fig. 40 shows another and very common form of a one-coil 
electromagnet. 

In this form the core forms the yoke and is fitted with two end 
plates, B and B, secured to it, in which opposite poles are produced. 
These poles in turn induce opposite polarity in A and the armature 
is attracted. This is a very compact form and is used largely in 
resistances for starting motors and other appliances. 

Fig. 41 shows another form of one-coil electromagnet, known as 
the iron-clad type. 

In this form the iron core is secured to and inside the bottom of 
a pot, and on the core is slipped the bobbin containing the wind- 
ing. The upper end of the core forms one pole while the whole 



128 



Naval Electricians' Text Book 



upper rim of the pot forms the other, and the armature consists of 
a disc or lid of the same diameter as the pot. 

All the foregoing types of electromagnets are examples of forms 
capable of exercising a strong pull over a short range. 

For a weak pull over a long range, the ordinary solenoid with 



a movable core is used, as shown in Fig. 42. 



m 



r _A_ 


71 


.S 


B 


.5 


n 




fi 


m 


lllllilllllllliiii! 






c| 


L " D"" 

|c 




J 


Winn in 


II 




l___y— -I 





Fig. 42. — Long-Range 
Electromagnet. 



Fig. 43.— Stopped 
Solenoid. 



When current is sent through the coils of this electromagnet, the 
core is sucked into the coil and the pull is greatest when the entering 
end reaches the further end of the coil. The pull in this form is 
not nearly as great as the form of Fig. 37, but the range of motion 
is very much increased. 

Double Magnetic Circuit. — A modification of the above is shown 
in Fig. 43. 

In this the magnetizing coil is slipped over a short core, E, which 
is secured to the yoke, Y , which is also provided with two limbs, 
n and n. The armature, A, is of the ordinary shape and is secured 
to a core, B, which is sucked into the coil when current is turned 
on. The dimensions are such that the bottom of D comes up 
against the top of E just when the armature brings up against the 
limbs n and n. This arrangement produces a double pull as the 



Magnetism and Electro:magnetism 129 

magnetic field is divided, as the magnetic lines through B and E 
divide at the yoke and pass through the limbs n and n then through 
the ends of A to B again. 

These last two forms are used in the mechanism of electric arc 
lamps and in some forms of automatic starting resistances for 
electric motors. 

Magnetic Circuit. 

By a magnetic circuit is meant the path of the magnetic lines of 
force, and it has been shown that these lines tend to make closed 
curves, either passing entirely through magnetic substances or 
partly through them and partly through air. Whatever the form 
of the magnetic circuit, its function is to direct the lines of force 
and the material of the circuit governs the resistance offered to the 
flow of the magnetic lines. Although these lines have no material 
existence, yet they can best be explained by their analogy to the 
electric current and considered as actually -flowing in the magnetic 
circuit. In the magnetic circuit there is a leakage of the lines of 
force just as in the electric circuit there is a leakage of current. 

The total number of lines in a magnetic circuit is generally 
referred to as the magnetic flux. 

Magnetic Potential. — It has been shown that an electric current 
cannot exist in a conductor unless there is a difference of electric 
potential between the ends of the conductor, and there can be no 
magnetic lines of force produced unless there is a difference of 
magnetic potential. 

Magnetic potential is measured by the work done in moving a 
unit magnet pole against the magnetic forces, and it has been shown 
that the magnetizing force due to a solenoid is 

work done = -yr — ergs, 

where C z= current in amperes, 

8 = number of turns of conductor on the solenoid. 

As the magnetic potential is equal to the work done against the 
magnetic forces, it follows that it is equal to the magnetizing force 
of the current, or 

the magnetic potential = — r^ — . 



130 Naval Electricians' Text Book 

To complete the analogy to the electric current, the magnetic 
potential is given the name magnetomotive force, and is defined 
as that force which tends to force magnetic lines through a mag- 
netic circuit. It is designated as M. M. F. 

The expression for M. M. F. contains only the variable factors, 
C and S, and is therefore directly proportional to their product 
CS, an expression which is called ampere turns. Experiment shows 
that as long as the number of ampere turns is constant, the M. M. F. 
will be constant; that is, one turn of conductor carrying 100 am- 
peres will produce the same magnetization or M. M. F. as 100 
turns carrying one ampere. It is also immaterial how far apart or 
how close together the turns are wound, the resulting M. M. F. will 
be the same. 

Law of Magnetic Circuit. — Just as in the electric circuit, we 

have the law that 

total E. M. F. 

total current = m =-r * 

total resistance ' 

in the magnetic circuit we have 

total M. M. F. 



total number of lines 



total magnetic resistance * 

The total number of lines of force that a given magnetomotive 
force can force through a magnetic circuit depends on the magnetic 
resistance of the circuit, and this magnetic resistance is called its 
reluctance. 

The magnetic law can now be stated in words, that the magnetic 
flux in any magnetic circuit is directly proportional to the mag- 
netomotive force and inversely proportional to the reluctance, or 
in symbols, 

^ T M. M. F. 

N =— z— ■ 

Reluctance. — This property of a magnetic material depends not 
only on the substance itself, but on its dimensions, varying directly 
as its length and inversely as its area of cross-section. It also varies 
inversely as its permeability, the higher the permeability, the less 
its resistance to the magnetic lines. For any portion of a magnetic 



Magnetism axd Electromagxetism 



131 



circuit, the reluctance of any portion is given by the expression 



Z = 



l_ 



where 



and 



Z = reluctance, 
I =. length of the path in centimetres, 
a = cross-sectional area in square centimetres. 

If, as generally the case, there are air gaps in a magnetic circuit, 
the reluctance of the whole is much increased, due to the low per- 
meability of air ; the reluctance also depending on the dimensions 
of the air gap. 




Fig. 44. — Typical Magnetic Circuit. 



Joints also increase the reluctance, the amount of increase being 
a matter of experiment for each particular kind of joint. 

Great heat increases the reluctance, but the temperature at which 
this is manifested is very seldom met in ordinary magnetic circuits. 

Typical Magnetic Circuit. — In many combinations of electro- 
magnets there are one or more magnetic circuits, but the data for 
each one may be determined separately, and the total joint effect 



132 Naval Electricians' Text Book 

calculated. Examples of magnetic circuits will be shown later 
under the head of fields of dynamos and motors, but a typical cir- 
cuit is inserted here. 

Fig. 44 shows a typical four-pole magnet frame, in which there 
are four closed magnetic circuits. One of these fields is represented 
by the dotted line, through the magnet frame, the core pieces, the 
pole pieces, the air gaps, and the armature. 

If a = area of cross-section of the different 
parts shown, 

I = length of corresponding parts, 
H = coefficient of permeability of 
corresponding parts, 
then the reluctance 



from A to B 



B to G and A to H = 



i j d a d 



C to D and H to G = ~~ , 

D to E and G to F = — *— , /x = 1 f or air. 

E toF =\- 

If all the magnetic parts of the circuit are of the same material 
f*a — p-b = y-c — m • 

If the magnetic field is due to a current of C amperes with S 
turns, then the full expression between the magnetomotive force, the 
reluctance, and the total number of lines N is, assuming the same 
material, 

4.7ZCS 



N= 



\ixa a "*" a a "f" ^s" 1 " /*« "^ /*W 



To this denominator should be added the reluctance of the joints, 
which being known by experiment N can be calculated for a given 
number of ampere turns, or N being known from the E. M. F. to 
be generated, CS the necessary number of ampere turns can be 
calculated. 



Magnetism axd Electromagnetism 133 

Residual Magnetism. 

Suppose a piece of soft iron which exhibits no, or practically no, 
magnetism is made the core of a solenoid. When current is sent 
through the solenoid, the core at once evinces strong magnetic 
properties, due to its permeability. If now the solenoid current is 
turned off, it is found that the soft iron will now show magnetic 
properties, although in all other respects it is the same as before. 
The magnetization that is left in the iron is called residual mag- 
netism, and the property of acquiring residual magnetism is called 
retentivity. The amount of magnetism retained after the mag- 
netizing force is removed is called remanence. If the magnetizing 
current is reversed, the remanence disappears and if the current is 
the same as before, the core will be as highly magnetized with the 
opposite polarity. The force necessary to reduce the remanence to 
zero is called the coercive force, being a fraction of the total 
magnetizing force. 

Certain substances show more residual magnetism than others, 
soft annealed iron showing much more than hard iron or steel, 
though the latter substances will hold their magnetism longer than 
the former, requiring a greater coercive force. Eesidual mag- 
netism is greater when the current is gradually diminished, for 
when it is suddenly turned off there is a momentarily induced 
current of opposite direction which tends to destroy the residual 
magnetism. Mechanical shocks or changes of temper affect residual 
magnetism, especially in the softer varieties of iron, a gentle tap 
at times being sufficient to destroy it. Eesidual magnetism also 
gradually disappears in time, though varieties of hard iron or steel 
will nearly always show traces of it. 

Measurement of Magnetic Fields. 

In measuring the strength of a magnetic field what is desired is 
the total intensity of the field, and is calculated from the formula 
previously given 

B — 4irl + H, 
or 

1 — 4- 



134 Naval Electricians' Text Book 

It is not necessary to make an exact measurement of the magnetic 
fields of dynamos on board ship, so the method of investigation 
will only be hinted at, exact methods requiring the use of instru- 
ments only found in laboratories. A small induction coil is con- 
nected to a ballistic galvanometer with its plane at right angles to 
the direction of the field. This is suddenly withdrawn to a place 
where the field is sensibly zero, when a deflection of the galvano- 
meter needle is produced, owing to the current induced in the coil. 
This deflection is compared with the throw obtained by turning 
over quickly a large induction coil lying horizontally in the earth's 
field, this throw being proportional to the earth's vertical force. 

It is frequently of importance to know how far the action of a 
magnetic field of a dynamo is felt from the machine, or to investi- 
gate the stray field of a generator ; that is the lines of force that do 
not pass through the armature, and are not available for the induc- 
tion of currents. This may readily be done by the vibration of an 
ordinary horizontal compass needle. 

A compass needle when at rest, and only under the action of the 
earth's force, will point to magnetic north and if drawn aside from 
that position will vibrate from one side of north to the other, the 
arc of the angle described gradually lessening until the needle is 
again at rest and points north. During this time, the needle will 
make a number of vibrations depending upon the strength of the 
earth's horizontal force at that place. If now this same needle is 
made to vibrate in some other magnetic field, as the stray field of 
a dynamo, it will vibrate under the combined action of two forces, 
that of the stray field in addition to the earth's field. The square 
of the number of vibrations is proportional to the force under which 
the needle vibrates, and if the number of vibrations is counted for 
the same interval of time in the two cases, the forces are propor- 
tional to the squares of the number of vibrations in that time. 

If n is the number of vibrations due to TL, the earth's hori- 
zontal force, and n' the number due to the combined forces E r 

then H' = SlL. . The nearer ri approaches n the nearer B' ap- 

n 2 
proaches H. The needle may be vibrated at different distances 
from the dynamo or motor, and the combined forces of the earth 



Magnetism axd Electromagxetis^i 135 

and machine may be calculated in terms of H, and the point noted 
where n' becomes equal to n, when H' = H, or the influence of the 
field has disappeared. This will give the distance in one direction 
where the stray field is zero, and the operation can be repeated in 
different directions. In making these experiments, the field of the 
machine should be excited to its fullest magnetization so the extreme 
distance will be known at which any external field exerts influence. 



CHAPTER VIII. 
ELECTROMAGNETIC INDUCTION. 



Induction as used in electromagnetism may be defined as the 
mutual reaction that takes place between a magnetic field and a 
current of electricity flowing in a closed conductor lying in the 
influence of that field. It is immaterial in what manner the field 
is produced, and it may even be produced by the current of elec- 
tricity itself, in which case the mutual action takes place between 
the current and the field that is produced by it. 

It has been shown that currents of electricity flowing in closed 
conductors set up around the conductors magnetic fields, which 
are uniform in strength as long as the current is steady. Unless 
influenced by some external magnetic disturbance, the magnetic 
lines will be constant in number, direction, and position just as 
long as there is no change in the strength of the current. The 
intensity of this field will change as the current starts, stops or 
in any way alters its rate of flow. 

If now there is a closed conductor without current, and by any 
means external to the conductor, a magnetic field is set up around 

it, it will be found that there is indication 
of current in the conductor as long as 
there is any change in the intensity of the 
field around the conductor. When once 
the field around the conductor is constant, 
then indication of current in the con- 
ductor ceases, although the field still sur- 
rounds it. 

Suppose we have a closed conductor a, 
t, c, of the shape shown in Fig. 45, the 
circuit being completed around a small 
Fig. 45.— Electromagnetic compass needle n, s, pivoted at 0, the 
Induction. whole so arranged that the conductor 




Electromagnetic Induction 



13' 



and connecting wires are parallel to the needle. If a pole of a 
permanent magnet N is thrust into the ring formed by the con- 
ductor, the magnetic lines due to this magnet spread out as shown 
in the figure, some passing through the conductor and others pass- 
ing through the space enclosed by it. This magnetic field reacts 
on the conductor, setting up around it a magnetic field which in 
turn produces a current in the conductor. This process is called 
induction, and the current induced is manifested by the needle, n, 
s being deflected, due to the induced current flowing around it. 
This induced current is only noticed during the time that there is 
relative motion between the field of the magnet and the conductor, 
for as soon as the magnet is held steady in any one position, 
although the intensity of the field remains the same, there is no 
manifestation of current. The energy of pushing the magnet 
towards the conductor has been converted into electric current and 
when the magnet is at rest, there is no energy expended and no 
currents induced. 

If the magnet was held steady and the conductor pulled away 
from it, there would be the same phenomenon exhibited, except that 
the needle would be deflected in the other direction. Approaching 
the south pole would produce a current in the opposite direction 
from that induced by the approach of the north pole. 

The nearer that the pole is approached to the plane of the con- 
ductor, the greater is the deflection of the needle, showing greater 
current induced as more lines of force from the magnet pass 
through the coil. 

Fig. 46 shows how more lines would 
pass as the magnet is approached nearer 
and nearer. 

This experiment illustrates the first 
principle of induction, showing that 
currents are induced in closed coils 
through which lines of force of an 
external magnetic field pass, as long as 
there is such relative motion between 
them as to alter the number of lines 
that pass through the coils. Fig. 46. 




138 Naval Electricians' Text Book 

The direction of an induced current in a closed coil depends 
upon the direction of the lines relative to the movement of the 
conductor, upon the number of lines and whether the motion tends 
to increase or decrease the number of lines that pass through the 
coil. As it is important to know the direction of induced currents 
under certain circumstances, the rules for determining this direc- 
tion or the laws of induction, as they are called, are given. 

Determination of Direction of an Induced Current. — One of the 
simplest and most easily remembered rules is that given by Fleming, 
as follows: Arrange the thumb and first two fingers of the right 
hand to point in three directions at right angles to each other. If 
the first finger points in the positive direction of the lines of force, 
and the thumb in the direction of the motion of the conductor, then 
then middle finger will point in the direction of the induced current. 

Laws of Induction. — 1. A decrease in the number of lines of 
force that are cut by a closed coil produces a direct current, that 
is, a current of such direction, that if one looks along the positive 
direction of the lines of force, it will flow in the closed coil in the 
direction the hands of a clock move, or clockwise. 

2. An increase in the number of lines of force that are cut by a 
closed coil produces an inverse current, that is, a current of such 
direction that if one looks along the positive direction of the lines 
of force, it will flow in the closed coil in a direction opposite to 
that of the hands of a clock, or anti-clockwise. 

3. The E. M. F. generated is proportional to the rate of decrease 
of the number of lines of force cut. 

If the N pole of the magnet referred to above is thrust into the 
ring at right angles to the plane of the paper from the near side 
of the paper, there is an increase in the number of the lines that 
pass through the coil and the observer on this side of the paper is 
looking along the positive direction of the lines of force, so the 
resulting current is inverse or anti-clockwise as viewed by the 
observer. The effect of this induced current is to make the near 
side of the coil a magnetic shell of north polarity. We then have 
the effect of a north pole approaching a north pole, which produces 
repulsion between them and which is manifested by its requiring 
greater force to thrust in the magnet as it approaches the coil. 



Electromagnetic Induction 139 

In pulling away the magnet (N pole) from the coil or the coil 
from the magnet (N pole), there is a decrease in the number of 
lines of force that pass through the coil, and still looking along 
the positive direction of the lines of force from this side, the result- 
ing current is direct, or clockwise, tending to make this side of the 
coil a shell of south polarity. We have now the effect of a north 
pole being pulled away from a south pole or vice versa, causing an 
attractive force between them, which is manifested in the greater 
force required to separate them. 

Lenz's Law. — This phenomenon of induced currents is summed 
up in Lenz's law, which states that " in all cases of electromagnetic 
induction, the induced currents have such a direction that by 
their reaction, they tend to stop the motion which produces them." 

Illustration of Induction. 

As a further illustration of the laws of induction suppose we had 
a circular closed coil lying in a magnetic field, the plane of the 
coil being at right angles to the lines of force and so arranged that 
the coil could be revolved about the extremities of one of its 
diameters. 




Fig. 47. — Illustration of Induction. 

In Fig. 47 the lines of force are represented by the dots running 
through the paper, the observer on this side looking along the 
positive direction of the lines. As long as there is no movement of 
the coil, there is no induced current. Imagine the coil to be re- 
volved on the axis a, ~b, the upper half turning into the paper, then 
there is a decrease in the number of lines that pass through the 
coil, and from the first law of induction, the induced current should 
be in the direction shown by the arrow. Xow the converse of this 



140 Naval Electricians' Text Book 

is also true, and if a current flows in the direction of the arrow, 
then the resultant field, within the coil, has the direction shown 
by the positive direction of the lines. A free north pole would be 
repelled from this side of the paper, showing that this side is of 
south polarity, a fact previously shown as due to a clockwise cur- 
rent. The field due to a current flowing in the conductor in the 
direction of the arrow is not the same as the imaginary field above 
consisting of parallel straight lines, but the resultant field, within 
the coil, may be imagined to be represented by one line, shown by 
the heavy dot and marked IN, that being its positive direction. 

From the above it is seen that there is the same relative connec- 
tion between the directions of the lines of force and the resulting 
induced current as there is between a steady current and its result- 
ant field. 




Fig. 48. — Illustration of Induction. 

If, instead of approaching a magnet with its lines of force issuing 
in all directions to our closed coil, suppose we imagine this coil to 
be thrust into a uniform magnetic field as represented in Fig. 48. 

The magnetic field is represented as before by the dots, and the 
observer is looking along the positive direction of the lines of force. 
As the closed coil a, c is moved from left to right into and at right 
angles to the magnetic field, there is an induced current in a, c due 
to the change in the number of lines that pass through the coil. 
It has already been noted that for the induction of current, there 
must be a change in the number of lines passing through the coil. 
If the coil is moved up and down the plane of the paper while 
lying in the field, there will be as many lines entering the coil on 



Electromagnetic Induction 



141 



one side as are leaving it on the other, so there will be no change 
and no induced current. Similarly, if the coil while parallel to the 
plane of the paper is moved up and down through the paper, there 
will be no induction. The above phenomenon is noticed when there 
is no change of intensity of the field, for if the number of lines at 
any portion is greater than at another, there will be a change in 
the number of lines passing through the coil, and so there will be 
induction of current. 



r 



Fig. 49. — Illustration of Induction. 



If the coil while lying at right angles to the lines was revolved 
about one of its diameters, there would be induction, for the number 
of lines that passed through the coil would then vary from a 
maximum to a minimum. 

Suppose now the conductor a, c instead of forming a closed coil 
is straightened out and forms a long straight conductor, so in the 
sense we have been speaking, there is no closed coil. This is 
represented in Fig. 49. 

If this straight conductor a, c is moved from left to right at 
right angles to the magnetic field and into it, it will be found that 
there is an induced current precisely as in the case where the con- 
ductor was bent into a circular coil. Here the induced current 



142 Naval Electricians' Text Book 

cannot be said to be due to the change in the number of lines that 
pass through the coil, for there is no coil, but the current is in- 
duced by the conductor cutting the lines of force. If the conductor 
is moved parallel to the lines there is no cutting and no current. 

This illustrates the principle of induction that a conductor 
moved across a magnetic field so as to cut the lines of force, there 
is an E. M. F. generated which tends to produce an induced cur- 
rent in that conductor. If the cutting be made continuous a con- 
tinuous induced current will be the result. 

The distinction between the currents induced in a conductor by 
a change in the number of lines that pass through the coil and by 
a conductor cutting across lines of force is not so sharp as it might 
appear. The induced current in either case is due to the same 
movement, and every conductor carrying a current forms part of a 
closed circuit, and while a conductor may be cutting lines of force, 
yet those lines must be passing through a closed coil of which the 
conductor is part, and the lines are passing into and out of the coil 
at the exact rate that the conductor is cutting them. The distinc- 
tion is made between the two, as some examples of induction are 
better explained by one method and others by the other, and the 
application of both should be understood. 

In either case, it is not a current that is generated, but rather 
an E. M. F. and we speak of the generation of E. M. F. and the 
induction of current, the latter following as a result of the former. 

Different Methods of Induction. 

As a result of induction, an E. M. F. may be generated in a 
closed conductor, or currents may be induced in it, by three differ- 
ent methods ; that is, by electromagnetic induction, by self-induc- 
tion and by mutual induction. 

In electromagnetic induction, as already explained, the change 
in the number of lines of force which pass through the closed con- 
ductor is due to some relative movement between the conductor 
and the magnetic field. This is the underlying principle of all 
dynamo electric machines. 

In self-induction, the change in the number of lines of force is 
caused by changes in the current that is producing the field, and 



Electromagnetic Induction 143 

any change produces a corresponding E. M. F. which opposes that 
change and which tends to keep the current at a constant strength. 
In dynamos and motors self-induction takes place in the coils of 
the armature that are passing under the brushes, in the positions 
in which the current is reversed, or is dying out, or starting in the 
other direction. 

In mutual induction, there are two or more closed conductors, in 
which any change in the field of one due to any change in its cur- 
rent acts on the other to increase or decrease its field, and conse- 
quently its current. The action is mutual: one acts or reacts on 
the other. This is the principle of the transformer or induction 
coil, or of a dynamo in which there is no moving part, the number 
of lines cut by one conductor being caused by changes of current 
in the other. 

Self-Induction. 

This is a case of induction in which an electric reaction takes 
place between a magnetic field and the electric current which pro- 
duces the field. This action prevents the instantaneous rise and 
fall of a current in a closed conductor. While the phenomenon of 
self-induction is almost imperceptible in the case of a simple con- 
ductor carrying a current, yet the principle may be pointed out by 
means of a straight single current and the magnetic field brought 
into existence by it. It has been shown that the magnetic field due 
to a current flowing in a straight conductor surrounds the con- 
ductor as a series of concentric rings or whirls, the number of lines 
of force remaining constant as soon as the current reaches a steady 
value ; the number increasing or decreasing with the current. When 
there is no current there is no magnetic field, but as soon as the 
faintest current flows, the lines of force are brought into existence. 
These lines of force may be considered as waves expanding from 
the very center of the conductor as a source of disturbance, and in 
their expansion they thread through or cut the conductor, and here 
is produced a simple case of electromagnetic induction, there being 
relative motion between the conductor and the field produced by the 
current. This current induced by the field, which in turn is pro- 
duced by the original current, is in the opposite direction to that 



144: Naval Electricians' Text Book 

of the original current and tends to weaken it, or to delay the 
current in reaching its maximum value. 

As long as the original current is increasing, the lines of force 
are expanding as a series of waves and the current is being con- 
stantly retarded by the induced current, but as soon as the current 
becomes steady, there ceases to be relative motion between the field 
and the conductors and the induction ceases. 

If the current becomes weakened the lines of force tend to col- 
lapse on the conductor, and this cutting of the conductor by these 
lines induces a current in the same direction as that of the original 
current, and which tends to keep the current from weakening. If 
the current is suddenly stopped, there is a quicker motion to the 
lines of force and this induced current may have an instantaneous 
appreciable value. 






hf 13 

Fig. 50. — Forms of Self-induction Circuits. 

The E. M. F. of the momentary induced current may have a 
value considerably higher than that of the original current, and it 
is this high E. M. F. which produces the spark noticed whenever 
a circuit is broken, for the induced current tends to flow, though 
the original current be broken, and the high E. M. F. generated 
tends to bridge over the circuit where broken, volatilizing portions 
of the metal circuit and maintaining an arc for a brief interval 
across the space where the circuit is interrupted. 

Forms of Inductive Circuits. — The amount of self-induction of 
an electrical circuit depends on its geometrical form. Eig. 50 
shows some forms of typical circuits. 

Type 1 shows that a current entering one of the terminals flows 
as many times around the helix in one direction as it does in the 
opposite direction, and in consequence the magnetic field set up by 



Electromagnetic Induction 145 

one series of convolutions is counteracted by that of the other 
series and there is practically no self-induction. This is known as 
a non-inductive resistance and the double winding is used for the 
coils of standard resistances. 

Type 2 shows very little self-induction but type 3 shows more. 
If the conductor of type 3 be made of many turns of wire close 
together, the effect of self-induction may be very marked. It will 
be still more marked if these turns are wound on an iron core, as 
type 4, as in the case of an ordinary electromagnet, for then there 
are many more lines of force due to the permeability of the metal. 
The lines of force in expanding from and collapsing on the con- 
ductor as the original current is increased or decreased, not only 
cut the portion of the conductor from which they emanate, but also 
the turns lying on either side for a considerable distance, so the 
total effect is that of all the lines of force due to each turn cutting 
a great many of the other turns. 

Coefficient of Self-induction. — The number of lines of force pro- 
duced by a current is directly proportional to the current in a region 
where the permeability of the surrounding medium is constant, and 
any change in the current produces a proportional change in the 
number of lines of force. 

A circuit has unit inductance when a rate of change of current 
of one C. G. S. unit per second produces one C. G. S. unit of 
E. M. F. One C. G. S. unit of E. M. F. is produced by the cutting 
of one line of force per second. Hence, the elements of current 
and number of lines are connected by the inductance, L, and since 
the number of lines is proportional to the current, we have the 
following relation: 

l- v . 

This coefficient, L, is constant for all values of C and depends 
on the form of the circuit. In a magnetic substance, the permea- 
bility varies with the current, and therefore L will vary with the 
degree of magnetization. 

If a coil has S turns, the total cutting of magnetic lines is SN, 
and 

LC = SN. 



146 Naval Electricians' Text Book 

Since in circuits without magnetic cores, N is proportional to S, 
L must be proportional to S 2 . The retardation of the current 
whether increasing or decreasing varies directly as the square of the 
number of turns of the conductor. The retardation in a coil of 
100 turns would be 100 times as great as in a coil of 10 turns. 

Since 

N = -ttt^- (see Magnetic Circuit) 
L = TrTy- C. Gr. S. units, 



or 



= 10 10 Z henries * 



Mutual Induction. 

The phenomena of self-induction and mutual induction are 
explained by the same electrical principles; self-induction being 
manifested in a closed conductor, the induction taking place in 
itself, while in mutual induction, the induction takes place in some 
adjoining separate closed circuit. However, the phenomenon of 
mutual induction may be accompanied by self-induction. 

Suppose there are two parallel conductors, A and B, Fig. 51, 

each forming a portion of a closed 
circuit. If in A current is estab- 
lished from some outside source, the 
usual magnetic field will be set up 
around it. As current flows, the 
lines of force will expand as waves 
from the conductor as a source of 
disturbance, and if the current is 

flowing in the direction marked IN, 
Fig. 51. — Illustrating Reversal .- ... ,. . . „., ... . 

of Current Due to Induction. the P 0Sltlve directl0n of the lines of 

force would be clockwise as shown by 
arrow 1. These waves expand, provided the current in A increases, 
until the conductor B is reached which up to this time has no 
current flowing in it. Immediately B acts as a new center of dis- 
turbance and a series of waves expand from it, the positive direction, 




Electko^iagxetic Induction" 



14; 



however, being now opposed to that due to A. Setting up these 
lines around B has the effect of inducing a current in B which is in 
existence until 'the current in A becomes steady. A change of cur- 
rent then in A has resulted in a momentarily induced current in B, 
but of the opposite direction. 

It is impossible to depict by diagram just how or why this re- 
versal of the positive direction of the lines of force takes place, 
when the current in one is increasing, but if the analogy of the 
lines of force to water waves be accepted, it is readily shown. 

But first suppose, however, that the current in A is steady and 
that the field due to this current embraces or surrounds B. If the 
current in A is now weakened, the lines of force surrounding A will 
collapse on A and in doing so will 
cut through B, which will become 
a center of disturbance of another 
series of lines, which will expand 
as long as those of A collapse, but 
which will disappear as soon as the 
current in A becomes steady. This 
is shown in Fig. 52. The lines of 
force of B will in this case have 
the same positive direction as those 
of A, showing that the induced cur- 
rent in B is in the same direction 
as the original current in A. 

The following figures, 53, 54, 55, and 56, are intended to show 
how in one case the direction of the wave lines, the lines of force, 
are in the opposite direction to the original lines and in the other 
case how they are in the same direction. 

Fig. 53 represents a wave as emanating from A and travelling 
in the direction of its normal, shown by the long arrow towards B; 
that is, it is expanding. The wave front on the left is shown as 
striking an obstacle B and its onward motion carries the outer part 
onward, the part near the obstacle being retarded. The arrows 
show the positive direction of the lines due to the current in A. 
The wave front bends around B until it is torn apart, as it were, 
when the wave front unites, with its positive direction the same 




Fig. 52. — Illustrating Reversal of 
Current Due to Induction. 



148 



Naval Electricians' Text Book 



as before, leaving a small wave around B in the opposite direction, 
as shown by Fig. 54, this small wave then expanding around B as 
the other dio\ around A, but with diminished energy. Each suc- 
ceeding wave from A is acted upon in the same manner, forming a 
succession of waves around B. 





Fig. 53. 



Fig. 54. 





Fig. 55. 



Fig. 56. 



Fig. 55 represents a wave as emanating at A and travelling in 
the direction of its normal, shown by the long arrow; that is, it is 
collapsing on A. The wave front on the left is shown as striking 
an obstacle B. Similar to the above, it is shown that the small 
wave set up around B is of the same direction as the collapsing 
wave. This small wave expands around B as shown in Fig. 56, 
inducing a current that is in the same direction as the weakening 
current in A. Each succeeding wave collapsing on A is acted upon 
in the same manner, forming a succession of waves around B. 



Electromagnetic Induction 149 

If both A and B have currents from some outside source flowing 
in them, any change in one will produce a change in its field which 
will react on the other, either increasing or decreasing its current 
as long as the change is taking place. 

Coefficient of Mutual Induction. — This is defined as the number 
of lines of force mutually embraced, or are common to both circuits, 
when each carries unit current. If L x is the coefficient of induc- 
tion of the first coil, called the 'primary, and L 2 of the second, 
called the secondary, then the coefficient of mutual inductance is 



M = V L ± L 2 . 

The coefficients of induction of each coil depends on the permea- 
bility of the surrounding medium, so, therefore does M, and the 
introduction of an iron core to the interior of one coil will greatly 
increase M. 

Mutual induction plays an important part in the principle of 
many electrical devices for the conversion of E. M. F. into higher 
or lower values. Prominent among these devices are Alternating 
Current Transformers and Induction Coils. 

Principle of Transformers. 

As in the case of self-induction, the mutual induction between 
two closed circuits will be greatly increased by making the con- 
ductors in the form of helices and winding them on some strongly 
magnetic material like soft iron, and bringing the turns on one 
close to those of the other. If under these conditions a rapidly 
alternating current be sent through one coil, it wdll produce a 
rapid expansion and contraction of its field which will produce a 
corresponding change in the current in the other coil. By making 
one coil of a great man}?- turns of very fine w T ire, a very high 
E. M. F. can be produced. By varying the size of the wire and 
number of turns in the two coils, a convenient method of changing 
the E. M. F. of a given source of supply is at hand. 

The elementary form of transformer consists of a closed mag- 
netic circuit, on which are wound the two coils, one called the 
primary; the other, the secondaiy, as shown in Fig. 57. 



150 



Naval Electricians' Text Book 



aaaaaaaa/vi 



A and B are the terminals of the primary and C and D of the 
secondary. The primary may consist of 
many turns of fine wire to receive a small 
current at high E. M. F. and the second- 
ary of a few turns of thick wire to give 
out a larger current at low pressure. Such 
a transformer would be called a " step 
down" transformer. If wound in the 
opposite sense, it would be called a " step 
up " transformer. 

Apart from the small losses in transfor- 
mation, the input is equal to the output, 
and if V is the terminal E. M. F. and C 
the current of one coil and V ± and C t of 
the other, then 




Fig. 57. — Typical 
Transformer. 



vc = V 1 C 1 



E and E x , the total E. M. F's. induced in each coil are directly 
proportional to the number of turns in the two coils. 

The relation between the voltages at the terminals is given by 
the following expressions : 

V = E -f- Cr (for primary), 
V ± = E ± — C x r 1 (for secondary) , 



*i 



= 1c (a constant depending on the relative 



number of turns) from which the relation of V to V ± may be found. 

V 



f -t-(f-^H 



Induction Coils. 

In the ordinary induction coil, it is not usual to use an alter- 
nating current, but a continuous current from a few cells, the 
change in the magnetic field of the primary coil being caused by 
making and breaking the circuit. The primary coil is connected 
in series with a condenser, which has the effect of making the 
" break " more rapid and opposing the current at " make." 



Electromagnetic Induction 



151 



The connections of a simple induction coil circuit are shown in 
Fig. 58. 

A represents the magnetic core around which are wound the two 
coils, the primary from the battery B; the secondary being wound 
over it, and carefully insulated. The terminals of the secondary 
coil are shown at a, b. The continuous current from the battery is 
interrupted at I, a pivoted conductor, which makes contact either 
with K or is drawn away from it towards the core A. When / 
makes contact with K and current from the battery flows around the 
primary coil, I is attracted to the core, breaking the circuit at K. 
As soon as the circuit is broken, the core ceases to be magnetic and 




Fig. 58. — Circuit of Induction Coil. 



I makes contact again with K, when the circuit is re-established. 
This constitutes the make and break and the alternating field pro- 
duced in the core induces an alternating current in the secondary 
coil, the current being manifested by a spark jumping from a to 6. 
The E. M. F. of the secondary coil depends on the rate of 



cUV 
dt' 



change of the magnetic field of the primary coil, as E = — 

where N is the number of lines of force. N depends on the 
primary current and t on the number of makes and breaks. When 
the interrupter I is attracted towards the core and the circuit is 
broken, the induced current produced by the break would ordi- 
narily cause a spark to jump from / to K, but by introducing the 
condenser in circuit, this extra induced current flows into it, charg- 
ing the upper plate positively, the lower, negatively. These charges 



152 Naval Electricians' Text Book 

immediately recombine, flowing through the primary and battery, 
thus reducing the battery current at the time the circuit is again 
made, and demagnetizing the core. This action increases the time 
of the " make'' while reducing the time of the " break/' making 
the latter quicker and sharper, the result of which is a high E. M. F. 
in the secondary. The terminals a and & can be so arranged that 
the spark due to break can jump across, while that due to make 
cannot, thus making a steady stream of sparks. 

Induction Coils for Creating Electric Oscillations. — In most sys- 
tems of wireless telegraphy an induction coil is used in the creation 
of electric oscillations necessary for the formation of electro- 
magnetic waves, and the following description is of a type suitable 
for such w r ork: 

Induction coils are known by their size, thus a 10-inch coil means 
that it will produce in air a spark 10 inches long between the 
terminals of the secondary coil. A coil of the above size would 
consist of 300 to 400 feet of insulated copper wire, wound around 
an iron core consisting of a bundle of soft iron wires about 2 
inches in diameter. The secondary would consist of 12 to 15 
miles of very fine double-covered silk copper wire, depending on 
the diameter, making 45,000 to 50,000 turns, wound over the 
primary. The winding of the secondary is made in a large number 
of sections, each section prepared separately and each carefully 
insulated with paraffin and discs of shellaced paper. A large num- 
ber of such sections varying from 100 to 500 are slipped over a 
thick ebonite tube, inside of which is the primary coil and iron core. 

When the coil is in operation great differences of potential exist 
in the coils of the secondary and this must be so wound that no 
two parts, which are a great difference of potential, are near to- 
gether. There must also be perfect insulation between the primary 
and secondary coils, and it is usual to have them separated by a 
tube of ebonite at least half an inch thick covered with a layer of 
paraffin an inch thick. 

When the sections of the secondary coil are assembled on the 
insulating tube they are compressed and immersed in molten par- 
affin. This is done on a former, after which the whole secondary 
winding is enclosed in a cylinder of ebonite and thick ebonite cheeks 



Electromagnetic Induction 153 

are fitted on the ends of the ebonite tube on which the secondary is 
wound. 

The completed coil may be then enclosed in a wooden box which 
is filled with insulating oil or filled in solid with paraffin, the 
ends of the secondary being brought out through ebonite tubes. 

If the coil is to be used with an interrupted continuous primary 
current, a condenser is placed across the point of rupture of the pri- 
mary current, its action being previously described. 

In some forms of induction coils, the primary is wound in sec- 
tions and the ends of each brought out in such a manner that the 
various sections can be joined in series or in parallel so as to vary 
the resistance and inductance of the coil, as well as the effective 
number of turns. 



CHAPTEE IX. 



ELEMENTARY THEORY OF THE ELECTRIC GENERATOR. 



An electric generator, or simply a generator, is a dynamo electric 
machine constructed for the purpose of converting mechanical 
energy into electric energy by the induction of E. M. F. in a closed 
coil moved in a magnetic field. 

Eeferring to the chapter on the Derivation and Definition of 
Units, the C. G. S. unit of E. M. F. is denned to be that E. M. F. 
produced by the cutting of a magnetic field of one gauss intensity 
by one centimetre of the conductor moving at a velocity of one centi- 
metre per second. 

In Fig. 59, the straight wire AD is fitted to slide along the 

portions AB and CD and to form 
portion of a closed circuit ABCD. 
The whole circuit is placed in a 
uniform magnetic field of in- 
tensity H, perpendicular to the 
plane of the paper with the posi- 
tive side on this side of the paper. 
If A D is moved to the right at 
a velocity of v centimetres per 
second, there will be an E. M. F. 
induced in .the conductor which 
will create a current in the direc- 
tion indicated by the arrows. If the length of AD is I centi- 
metres, then, according to the definition of E. M. F., the number of 
absolute volts induced will be 

E = Hlv. 

The E. M. F. induced produces a current which is urged across 
the magnetic field; the C. G. S. unit of current existing when each 




Fig. 59. — Illustrating the Principle 
of the Generator. 



Eleaiextary Theory of Electric Generator 155 

centimetre of its length is urged across a magnetic field of unit 
intensity with a force of one dyne. 

From Lenz's law it is seen that the work done in producing the 
induced current opposes the action which produces it, and the total 
force urging the conductor across the magnetic field is 

F = FLIC dynes. 

The work done on the conductor against this force is Fv ergs 
per second and which must be equal to the electric work produced, 
or 

Fv = HICv, 
or 

work done = EC ergs per second 
= EC watts. 

In the generator, then, work is supplied by an external agency 
moving a conductor across a magnetic field and continually over- 
coming a force which tends to stop it. The greater the current in- 
duced or the greater the intensity of the field, the greater the force 
to be overcome and the greater the power necessary to be supplied. 
Due to the mechanical construction of the generator, the force 
overcome is a tangential pull applied at the radius of the arma- 
ture, and the product of the two factors, force and radius, is called 
the drag on the conductors. If the conductor is supplied with an 
E. M. F. this drag on the conductor would cause the conductor to 
move in the opposite direction and the generator then becomes a 
motor. 

Expression of Induced E. M. F. — In t seconds the wire AD moves 
over a space equal to vt and cuts Ivt square centimetres. If the 
intensity is H; or, in other words, if there are H lines of force per 
square centimetre, the total number of lines cut is Hlut, and since 
E = Hlv 

N 

where N = total number of lines or magnetic flux. 

This shows that the induced E. M. F. is equal to the rate of 
cutting of the lines of force, or the E. M. F. in C. 67. S. units is 
equal to the number of lines of force cut per second. 



156 



Naval Electricians' Text Book 



Induced E. M. F. in a Closed Coil. 






In Fig. 60, N and S represent the north and south poles of a 
magnet, either permanent or electromagnetic, producing a mag- 
netic field that is represented by the lines running from one to the 
other, the arrowed heads representing the positive direction of the 
lines of force. In this field and lying at right angles to the lines of 
force is a rectangular loop of wire, its open ends being connected 
to a voltmeter, thus making a closed circuit, and capable of rotation 
round an axis represented by the broken line. 




Fig. 60. — Induced E. M. F. in a Closed Coil. 



As this coil lays at rest in the field there is no reaction between 
them, and the voltmeter indicates zero. In this position, being at 
right angles to the lines of force the greatest number of lines 
thread through the loop. As the coil is revolved as shown by the 
curved arrow to the right, the number of lines that thread through 
the coil constantly diminishes in the proportion of the angle turned 
through from 0°. If N is the total number, then at any angle 0, 
the number that threads through the loop is N cos (9, and at 90°, 
or when the loop is laying parallel to the lines, the number is a 
minimum. As soon as the coil is revolved so as to cut the lines of 
force, an E. M. F. is generated and it will be indicated on the 



Elementary Theory of Electric Generator 157 

voltmeter and if the coil is turned at a constant speed this E. M. F. 
will increase until the 90° position is reached when it is a maxi- 
mum. Xow applying the laws of induction, we see in what direc- 
tion the resultant current is ; for imagine the eve in the face of the 
north pole and looking along the positive direction of the lines of 
force. The voltmeter end of the coil will then be on the left hand. 
As the coil turns, the number of lines of force is decreased, and a 
decrease means a direct current or clockwise current when looking 
along the positive direction of the lines of force. In this case, the 
current would flow in the direction indicated by the straight arrow. 
As the coil passed the 90° position, there would be an increase in 
the number of lines, which should produce an inverse current, or 
anti-clockwise, as viewed by the same observer, but now he is look- 
ing at the other side of the coil, or what was the top is now the 
bottom, so, though it is anti-clockwise as he views it, it is really 
in the same direction in the coil as before. The E. M. F. will 
gradually decrease from 90° to 180°, where it will again be zero, 
and this will be indicated on the voltmeter. 

It must be remembered that the E. M. F. is not only proportional 
to the number of lines cut, but to the rate at which these lines are 
cut. At the 0° and 180° position, the greatest number of lines 
are being cut, but there the E. M. F. is least, and at 90° the lines 
thread through the coil at the greatest rate, at uniform speed, and 
here the E. M. F. is greatest, or the number of lines threading 
through at any time is N cos 6, and the rate of cutting is 
d(N cos 0) = — N sin 6, which is in accordance with the third 
law of induction, the minus sign indicating the decrease. The 
sine function varies from to unity, or the E. M. F. at 0° is 
sin 0° = and at 90° is sin 90° = 1, or proportional to these 
limits. Continuing the motion from 180° to 270° results in a 
direct current, or clockwise, and this is in direct opposition to the 
current in the first half of the revolution. From 270° to 0°, the 
current is inverse as viewed from the same place, but the coil now 
being turned over is in the same direction as from 180° to 270°. 

The final result then of one complete revolution of the coil is 
generation of E. M. F. and induction of current, starting at 0° 
with both a minimum and increasing to a maximum at 90°, then 



158 Naval Electricians' Text Book 

decreasing again, the current being in the same direction to 180°. 
From this point everything is reversed, the E. M. F. and current 
increases to a negative maximum, and then decreases to 0° as the 
original position is occupied. This result is both in accordance 
with the theory as deduced from the laws of induction, and is 
actually shown on the voltmeter, on passing the 180° position, the 
deflection of the needle being reversed. 

As the E. M. F. is proportional to the rate of cutting, the faster 
the coil is turned, the greater will be the maximum E. M. F., and 
greater in proportion at any intermediate position. 

It may be noticed that it is stated that the lines of force thread 
through the loop formed by the coil and the number of lines of 
force that do this first increase and then decrease. This is simply 
a convenient way of expressing the fact that the lines of force are 
actually cut by the coil in its revolution, and the mere fact that the 
lines of force thread through the loop would not necessarily mean a 
generation of E. M. F. It should also be noticed that the sides of 
the coil, the up-and-down connections, although they pass through 
lines of force, do not alter the number cut, so there is no E. M. F. 
due to these parts of the coil; they simply act as conductors to 
complete the circuit. 

Induced E. M. F. in a Closed Surface. — If this coil were replaced 
by a thin sheet of conducting material, the action and resulting 
current would be the same, with the exception that every part of 
the thin sheet would cut lines of force and the current would circu- 
late in all parts as small eddies, having a resultant effect of one 
large current, and would be reversed in exactly the same way as 
in the case of the coil. In this case also, there would be a real 
increase and decrease in the number of lines that pass through the 
sheet as well as an increase and decrease in the number of lines cut. 

Curve of E. M. F. 

As the E. M. F. generated in the preceding demonstration in- 
creases from to a maximum, then decreases to 0, and increases 
again to a negative maximum and then again to 0, there must be 
some constant relation between the E. M. F. generated and the 



Elementary Theory of Electric Generator 



159 



time of revolution. The relation is represented by the curve of 
sines, as the E. M. F. is proportional to d(N cos 6) = — N sin 6, 
and 6 depends on the rate of revolution. The curve of sines is the 
resultant motion of a particle that is acted on simultaneously by 
two motions, one a simple harmonic motion in a straight line and 
the other a uniform motion at right angles to it, and on account of 
its identity with the curve of E. M. F. its construction is given in 
Fig. 61. 



K 


N 


' 


— i 




K 


' 


























t N. 


i 




/ 






\ 


r 






















°~ \ 




'^ 










\ 


l!" 


















MM [ P/ItI 


o k 


I 




«. 


3 






b 


A 


I 




































\ 














/ 






















\ 










/ 








-J- 
















\ 


^ 


/ 


/ 







Fig. 61.— Curve of E. M. F. 



Curve of Sines. 

If a particle W revolves in the circle NESW at a uniform rate, 
in equal times, it will pass over equal arcs of the circle, and if the 
points at which the particle arrives at the end of equal intervals of 
time be projected on a diameter of the circle, the motion of these 
points on the diameter will constitute a simple harmonic motion. 

The curve of sines has been defined as the resultant motion of 
a particle that is acted upon simultaneously by two motions, one 
a simple harmonic motion and the other a uniform motion at right 
angles to the simple harmonic motion. 

The simple harmonic motion is represented as taking place in 
the line NO 8, the points a, b, c, and i\ 7 being the projections of 
the points arrived at in the circle by a particle that is uniformly 
revolving in it, the equal intervals of time in this case being 1-16 
of the time of one revolution. The uniform motion is taking place 
in the line WOE. In equal times the uniform motion carries the 



160 Naval Electricians' Text Book 

particle to the right equal distances, and the eqnal distances be- 
tween the vertical lines are arbitrarily chosen to represent the 
distance carried. 

Let the particle be at o' '; it is acted npon by two motions, a 
simple harmonic motion in the line N'O'S' and the uniform mo- 
tion in the line WOE. If the particle was acted upon by the 
simple harmonic motion alone, in 1-16 of the time of one period, 
it would be at a'. If acted upon by the uniform motion alone, in 
the same time corresponding to 1-16 of a period of the simple 
harmonic motion it would be at 1. As it is acted upon simulta- 
neously by these two motions, in 1-16 of a period, it would be at a" , 
describing the path o'a". Similarly in a time represented by 2-16 
of a period, in its simple harmonic motion it would be at V , and 
due to the uniform motion, it would be at 2, and as they act 
together, it would be at V , describing the path o'a"b". Similar 
reasoning will show how the points c"N"c"'b"'a"' , 8 are determined, 
and a curve drawn through these points will show the resultant path , 
of the particle. As the particle in its simple harmonic motion 
passes through 0', going towards S' , the uniform motion still 
acting, the part of the curve below the median line is described. 
When the particle has completed 16-16 of its period in its simple 
harmonic motion, it has been carried to the right 16 equal dis- 
tances, and the particle is in a position to repeat the described curve. 

Properties of the Curve. — The ordinates of the curve are propor- 
tional to the sines of the angles described by the particle in its 
uniform motion in the circle, the motion of this particle represent- 
ing the motion of the coil in the elementary dynamo. a"l is pro- 
portional to sin 0', b"2 to sin 0", etc. If the height of the middle 
ordinate iV"4 is unity, as the sine of 0"" or 90° equals 1, the heights 
of the other ordinates will represent, in terms of the middle ordi- 
nate, the sines of the angles formed at the center of the circle. 

The abscissae are proportional to the time during which the 
uniform motion acts, and which time being proportional to the 
arc of the circle swept over in the same time, is proportional to 
the sines of the angles thus described. As the ordinates are pro- 



Elementary Theory of Electric Generator 161 

portional to the sines of the angles, and the time to the sines of 
the angles, the equation of the curve must be y — sin x, the axis 
of Y representing sines and the axis of X, time. The area in- 
cluded between one quarter of the curve and the median line is 

/ 2 ydx or / 2 sin xdx, or area = — cos x~\* = — (0 — 1) = 1. 
As the length of the median line for a quarter of the curve is 

2~, the average value of the ordinates must be the area divided by 

1 2 
the base or — = — ; or, in other words, the average value of the 



7T 2 

sine function from 0° to -% must be—, or 7-11. Also the average 

2 
value of the heights of the ordinates must be — X the height of the 

maximum ordinate. 

In one revolution then of the coil in the elementary dynamo, the 

average E. M. F. is 7-11 of the maximum E. M. F. 



The Act of Commutation. 

It has been shown how a coil revolved in a magnetic field has 
an E. M. F. generated in it, and a current induced, and how in one 
revolution the current grows to a maximum, then decreases to a 
minimum, and then has the direction of the current reversed and 
the phenomena repeated. In continuous-current dynamos it is 
necessary that there be some means provided by which the current 
is made to flow in one direction in the external circuit, while it is 
reversed in each revolution in the internal circuit. This is effected 
by means of a commutator and the operation is called the act of 
commutation. Each end of the coil is secured to a segment of a 
circle, made of some conducting material, the segments being sepa- 
rated by air gaps or some- insulating material. These segments 
taken together constitute the commutator, on which rests the 
brushes, which collect the current for the external circuit. Just 
how the reversal is effected will be explained by small sketches 
showing the position of the coil in different stages of the revolution. 



162 



Naval Electricians' Text Book 



Fig. 62 represents the loop lying in the magnetic field between 
the pole pieces N and S, the lines of force running from N to S, 
and being omitted for sake of clearness. This loop is perpendicu- 
lar to the lines of force and in the 0° position, the brushes being 
shown as just touching both segments of the commutator and con- 
nected to the external circuit marked R. One-half of the loop is 
shown as a double line, being connected to its segment of the com- 
mutator, also double; the other half of the loop with its segment 
being shown as shaded, and they will be referred to as double and 
shaded. 




Fig. 62. — Act of Commutation, Coil at 0° Position. 



In this 0° position, there is no E. M. E. generated and no cur- 
rent induced. As soon as the coil is revolved in the direction of the 
curved arrow, E. M. F. is generated, and by the laws of induction 
current is induced and flows from double to shaded in the internal 
circuit, and from shaded to the external circuit through the + 
brush and from the external circuit to double through the — brush. 
This condition is shown in the next figure. 

In Fig. 63 the pole pieces have been removed but are supposed 
to be in the same position as in the first figure. This represents 
the loop in a position shortly after revolution has commenced, a 



Eleacextary Theory of Electric Gexerator 



163 



position a little in advance of the 0° position. A direct current as 
viewed by an observer looking along the positive direction of the 
lines of force is induced, or to the observer it is clockwise and flows 
from double to shaded in the internal circuit, from shaded to the 
external circuit through the + brush and from the external circuit 
to double through the — brush. The direction of the currents is 
indicated by the arrow heads. The brushes of course remain sta- 
tionary. When the revolving coil passes the 90° position, the 



27o*-- 




Fig. 63. — Act of Commutation, Coil Passed the 0° Position. 



shaded half is then uppermost, and there is an inverse or anti- 
clockwise current as viewed by the same observer, as there is now 
an increase in the number of lines of force cut, but the coil being 
turned over a direct current on one side and an inverse on the other 
makes the current in one real direction, and from 0° to 180°, the 
current in the internal circuit will be from double to shaded. 

This position of the loop (Fig. 64) shows it just before the 180° 
is reached. The current in the internal circuit is still from double 
to shaded and the external current remains as before. The current 



16-4 



Naval Electricians' Text Book 



is weakening as this position is reached and when it reaches the 
180° position, it will be the same as in the first figure, with the 
exception that the coil is simply turned over and the current both 
in the internal and external circuits has died out, and the brushes 
will just touch both segments of the commutator. Further revolu- 
tion from the 180° position will reproduce the phenomena of 
induction as in the 0° position with the exception of the coil being 
turned around. Following from 180° is shown in the next figure. 



*7°- - 




Fig. 64. — Act of Commutation, Coil Approaching the 180° Position. 



Fig. 65 represents the coil just after the 180° position is reached. 
There is now again a decrease in the number of lines of force cut, 
and a direct current for the same observer, but now the coil being 
turned half way around, the current flows from shaded to double 
in the internal circuit, from double to the external circuit through 
the -j- brush, and from the external circuit to shaded through the 
— brush. Thus it is seen that though the actual direction of the 
current in the coil is reversed, by means of the commutator the 



Elementary' Theory oe Electric Generator 



165 



direction of the current in the external circuit remains the same as 
before, and as far as its direction is concerned, it is continuous, 
which is the sole object of the commutator. The current will 
increase in intensity until the 270° position is reached. From that 
position to the 0° or 360° position, there is an increase in the 
number of lines of force cut, or an inverse anti-clockwise current 
as viewed bv the same observer, but what is now clockwise will 



476* 




Fig. 65. — Act of Commutation, Coil Passed the 180° Position. 



then be anti-clockwise and the real direction of the current in the 
internal circuit will be the same from 180° to 360°. 

Fig. 66 represents the loop just before the 0° or 360° position 
is reached. The current is now anti-clockwise as explained under 
the previous figure, but is still from shaded to double. The cur- 
rent is decreasing as the 360° position is approached until that is 
reached when the current has died out entirely, and the loop is in 
its original position, each brush just touching both segments of 
the commutator. 



166 



Naval Electricians' Text Book 



To summarize then : The current is nothing at 0°, then grad- 
ually approaches a maximum in both circuits until 90° is reached, 
then decreases to a minimum and becomes nothing at 180°, both 
currents having died out. From 180° both currents increase, the 
direction of the current in the internal circuit having been re- 
versed, while the current in the external circuit remains the same 
as before. This increase continues until 270° is reached when 



270: 




Pig. 66. — Act of Commutation, Coil Approaching the 360° Position. 

both currents are at a maximum again and then decrease of both 
currents takes place until the original position is occupied when 
both currents have completely died out. Further revolution of the 
coil repeats the phenomena. 



The Generation of an Increased and Steady E. M. F. 

It has been seen that a simple rectangular turn without a com- 
mutator when revolved in a magnetic field so as to cut lines of 
force gives rise to a fluctuating E. M. F., which in its complete 



Elementary Theory of Electric Generator 



167 



revolution is represented by the ordinates of the curve of sines, 
as shown by Fig. 67. Two revolutions are represented. 

If the coil is fitted with a commutator, the negative ordinates 
of the curve are commuted into positive ordinates as shown in 
Fig. 68. 




Fig. 67. — Curve of E. M. F. Before Commutation. 




40* <*0 470 

Fig. 68.— Curve of E 



M. F. After Commutation. 




Fig. 69.— Curves of E. M. F. Due to Two Coils. 



If, in addition to the simple turn, there is another turn placed 
at right angles to the first and connected to its own segments of 
the commutator, and entirely independent of the first turn, it will 
exhibit the same phenomena and give rise to the same curve of 
E. M. F. with the exception that it will differ in phase by one- 
quarter of a period, or the curves will differ in their maxima and 
minima by 90°. The result of two turns 90° apart is shown by 
Fig. 69, showing when one is in position of maximum cutting of 
lines of force, the other is in the position of minimum cutting. 



1G8 



Naval Electricians' Text Book 



If these two turns be connected in series with one another, or 
in other words, if the same length of conductor in the two turns 
be made into one coil with the two turns at right angles to each 
other, then the curve of E. M. F. in its entirety ceases to be the 
curve of sines, but the E. M. E. at any point is equal to the sum 
of the individual E. M. F's. at that point due to each turn alone. 



f i : ; !. i i i 'I : . j ! I ■ i i 

i ! ; ; ; ; i j j i j j j j j ! 

■ ' I i i • ! I ' j * i ■ | | ' 

,Vv k i-Vi : .: V ; I : V; I :\ 

O* TV •*»"' t? MS™ TIP IIP 77r? J^" O' 




Fig. 70. — Curves of E. M. F. Showing Superposition. 



In this case, the maximum E. M. F. would be at 45°, 135°, 225°, 
and 315°, and the minimum at 0°, 90°, 180°, 270°, and 360°. 

The result of superimposing the two curves formed by each turn 
of the coil, the turns being at right angles to each other, is shown 
in curve 1 of Fig. 70. The height of the ordinates at 0° and 90° 
of curve 1 is equal to the height of the ordinates at 0° and 90° 
of the original curve of E. M. F., these being shown at the bottom 
of the left-hand portion of the diagram. The height of the ordi- 
nates at 45°, 135°, 225°, and 315° is each equal to the sum of the 



Elementary Theory of Electric Generator 169 

ordinates at 45° of the original curves, or be of the curve 1 is 
equal to 2 X ab. 

Curve 1 then represents the E. M. F. due to one coil consisting 
of two turns at right angles to each other, connected in series, and 
has resulted in a mean E. M. F. of twice the original mean E. M. F. 

If another coil consisting of two turns at right angles to each 
other, and connected in series, he placed at equal distances "be- 
tween the turns of the first coil, it will give rise to another curve 
similar to 1, marked 2, having its maximum value where the other 
is a minimum and vice versa. If these two coils, or four turns, be 
connected in series, the resulting curve of E. M. F. will be curve 3, 
he being equal to oe -j- de, and nm = ne + em, or 2 X em. 

Curve 3 then represents the E. M. F. due to one coil consisting 
of four turns at angles of 45° to each other, all four turns connected 
in series, and has resulted in a mean E. M. F. of twice the value of 
curve 1, and four times the value of the E. M. F. due to one turn. 

If again another coil consisting of four turns at 45° to each 
other, and connected in series, be placed at equal distances between 
the turns of the other coil, it will give rise to another curve similar 
to 3, and marked 4. 

If these' two coils, or eight turns, be connected in series the result- 
ing curve of E. M. F. will be curve 5, pe being equal to ve -f- he, 
and su being equal to st -f- tu or 2tu. 

Curve 5 then represents the E. M. F. due to one coil consisting 
of eight turns, at angles of 22 J ° to each other, all eight turns con- 
nected in series, and has resulted in a mean E. M. F. of twice the 
value of curve 3, four times the value of curve 1, and eight times 
the value of the mean E. M. F. due to one turn. 

This process shows that the more conductors there are in series, 
the higher and steadier the E. M. F. and a point would eventually 
be reached when the curve would approximate a straight line, and 
this is really in fact the theoretical process of building up a drum- 
wound armature. 

The same steadiness without the increased E. M. F. would be 
observed if the eight turns, or sixteen cutting conductors were each 
connected to their segments of the commutator without in any 
way being connected to one another. The resulting curves are 



170 Naval Electricians' Text Book 

shown in the right-hand lower portion of the diagram, and it is 
seen that the E. M. F. is as nearly continuous as in the first case, 
but the E. M. F. is that due to one turn. If again these were all 
connected in series as before, the resulting curve of E. M. F. would 
be obtained at any point by addding together all the ordinates of 
the different curves at that point, and of course it should give 
the same curve as in the first case, where the additions take place 
separately. The height of the ordinate 5.11 is equal to 1.5 + 2 
X 2.5 + 2 X 3.5 + 2 X 4.5, and 10.12 is equal to 2 X 6.10 + 2 
X 7.10 + 2 X 8.10 + 2 X 9.10. 

Curve of Total E. M. F. 

The curve of sines represents by the heights of its ordinates the 
E. M. F. at any instant of a single turn of conducting material 
revolved in a magnetic field in terms of the maximum ordinate 
as unity. The total E. M. F. due to the same turn in one revolu- 
tion is the sum of all the ordinates, that is, the total E. M. F. 
from 0° to 45°, for instance, is the sum of all the ordinates from 
0° to 45°, or is represented by the sum of all the sines of the angles 
from 0° to 45°. In other words, it is the integration of the equa- 
tion of the curve from 0° to the point considered, or 

Jnz° -jz° 

sin xdx = — cos a; I 
o° Jo° 

The curve of total E. M. F. from 0° to 360° is represented by 
Fig. 71. 

Armature Cores. 

So far in the consideration of the physical theory of the genera- 
tor, the turn of wire was supposed to be revolved between the poles 
of a magnet, permanent or temporary, in the field produced by the 
poles, and without any mechanical connection with any other re- 
volving part. It must necessarily be wound on some kind of 
support and to this support the general name of core is applicable. 
As far as mechanical considerations go, this core might be made 
of wood or brass or hard rubber, but electrical considerations show 
that it should be of some magnetic material, in order that the lines 



Elementary Theory of Electric Generator 171 

of force may be drawn to and through it, or as it has been seen 
under magnetic circuit, in order that the reluctance of the magnetic 
circuit may be reduced. For a given magnetomotive force, due to 
the ampere turns of the field windings, the total number cf lines, 
or flux, depends on the magnetic resistance, and the smaller this 
can be made, the greater will be the flux. The conductors must 
cut the lines of force and to do this they must thread through one 
side of the core and out the other. If the core were of some non- 
magnetic substance, the lines of force would tend to go around it 
rather than through it, its permeability being less than that of air, 



O 10° l«0° ilo* 3bO 

Fig. 71.— Curve of Total E. M. F. 

the lines of force cut by the conductors being much reduced. 
Where a magnetic core is used, the magnetic circuit consists of the 
field frame, the pole pieces, the air gaps between the pole pieces 
and armature core, and the core itself. This shows, too, that the 
air gaps should be as small as possible, and the pole pieces should 
have a cross-section at least equal to the smallest cross-section of 
the magnetic circuit. 

Eddy Currents. — The core, being magnetic, while revolving in the 
magnetic field is subject to the same laws of induction as the con- 
ductors themselves, and would have induced in its mass currents 
which would flow around and through it, and in any one cross- 



172 Naval Electricians' Text Book 

section they would flow in the same direction. They follow the 
paths of least resistance in the core, thus giving rise to innumerable 
little complete circuits, to which the name of eddy currents is given. 
The effect of these currents is to heat the core, and being brought 
into existence by the power which revolves the armature they repre- 
sent a distinct loss of energy. It is remembered that the induced 
current has a direction which is at right angles to the magnetic 
lines, and if the circuit of the eddy currents can be shortened in 
that direction their waste will be reduced. This is effected by cut- 
ting the armature core in thin slices in a direction parallel to its 
direction of rotation and to the lines of force and perpendicular to 
the direction of the induced currents. The thin slices or lamina- 
tions are put together, being insulated one from the other, the 
effect being to reduce the eddy currents without increasing the 
magnetic resistance of the circuit. Any through connections there 
may be for holding the laminations together will have induced 
currents in them, but it is usual to have them well inside the core, 
where the field is weakest. 

Calculation of Induced E. M. F. 

The preceding curves show that an increased E. M. E. is pro- 
duced by connecting up the single coils in series, so as to make 
one closed coil of many turns. The number of conductors on the 
armature then becomes one of the factors that determine the value 
of the E. M. E. generated. Under the definition of volt, it was 
seen that it was the E. M. E. induced when a conductor moves in 
a magnetic field at such a rate that it cuts 10 s lines of force per 
second. The number of lines of force is then another factor of 
the generated E. M. E. The effect of cutting lines of force may 
be increased by increasing the speed at which the conductor moves, 
thus if a conductor moves at such a rate as to cut 2 X 10 8 lines of 
force per second, it will generate 2 volts and so on. 

The three factors that determine the E. M. F. in a dynamo are 
(1) the number of cutting conductors ; (2) the number of lines cut; 
(3) the speed at which the lines of force are cut. 

Starting with the elementary coil of the drum armature in the 
2-pole dynamo in a plane at right angles to the lines of force, it 



Elementary Theory of Electric Generator 173 

embraces the total 'number of lines, which may be represented by N. 
If this rectangle or coil makes one revolution per second there are 
2N lines cut per second by each limb of the coil, because each limb 
cuts the whole number of lines in each half revolution. If the coil 
makes n revolutions per second the number of lines cut per sec- 
ond by each limb is 2Nn. If there are Z conductors all the 

wa}^ around the armature, or Z limbs, there are -a~ limbs in series 

from brush to brush, or the number of lines cut by —% limbs is 

sr X 2Nn = NZn, or the average E. M. F. induced is -^- 
volts, where 

X — total number of lines of force, 

Z = total number of conductors around the armature, 

n = number of revolutions per second. 

In drum armatures, the number of limbs is twice the number of 
coils in each section, whereas in the ring armature, the number of 
limbs is equal to the number of coils in each section, and the same 
formula is applicable to both armatures. Z always represents the 
number of conductors counted all the way around the armature. 

The average E. M. F. may be expressed in terms of angular 
velocity by putting <o == 2 7m where w = angular velocity and then 

E = £rNZ. 

In a time t, the angle 6 turned through would be 2irnt and the 

number of lines enclosed by the rectangle at the angle 6 turned 

through from zero would be N cos 0, and the rate of cutting would 

be the rate of N cos 2-n-nt = 2-n-nN sin 0. The average of sin 6° 

2 
between 0° and 90° is—, so the average 

2 
E. M. F. = 2imN Xt- 4rciV. 

The number of rectangles is \Z and the number of conductors 
in series from brush to brush is -J X J^ or the final average 
E. M. F. = 4 X iZNn = NZn as before. 



174 Naval Electricians' Text Book 

Fundamental Equation of the Direct-Current Generator. — The 
above equations are adduced to apply to bipolar machines, but a 
more general solution for the value of the induced E. M. F. is 
given. 

Let N = the number of magnetic lines that enter the armature 
from each north pole and leave at each south pole of 
the field magnets, 
p = number of field poles, 

Z = number of conductors on the outside of the armature, 
p' = number of parts in parallel between brushes, 
n = number of revolutions of armature per second. 

In ~th of a second the armature will move the distance between 
jj Hi 

two poles, or between the brushes and in this time will cut N lines 

of force. The conductors are then cutting at an average rate equal 

to N -f- ~ , or pnN lines of force per second. The average E. M. F. 

from brush to brush per conductor is pnN at any instant. 

The number of conductors in series in each path between the 

brushes is— 7 and since the average E. M. F. per conductor is pnN, 

the E. M. F. between the brushes is pnN X -~zj , or 

E _ VnNZ 

v' 

This equation applies to bipolar or multipolar machines, and ring 
or drum armatures with any kind of winding, the above expression 
giving the E. M. F. between the brushes in absolute units. 

Points of Design. — In generators designed for use with direct- 
connected motive-power as with sets used on shipboard, the number 
of revolutions of the armature is limited by the speed that can be 
given to the engine and this is necessarily low. Increasing the 
number of conductors in series on the armature results in higher 
E. M. F., but at the same time adds to the resistance and to the 
self-induction, both of which are objectionable. Increasing the 
area of the armature conductors or making the core more massive 



Elementary Theory or Electric Generator 175 

increases the number of lines cut, and this is one of the features 
of modern dynamos, the cores being very large and the conductors 
few and heavy. The greatest factor of the E. M. F. is undoubt- 
edly the magnetic field, and this is the most practical way of 
increasing it. In modern machines, the field is made very strong 
and is divided up into many separate magnetic circuits, this having 
the advantage of increasing the E. M. F. and at the same time 
reducing armature reactions and distortion of the field, so there is 
very little necessity, if any, of changing the position of the brushes 
on changes of load. 



CHAPTER X. 
GENERATORS. 

A consideration of the elementary theory of the generator shows 
that in order to produce a continuous current in the external circuit, 
there must be (1) a magnetic field, (2) a collection of conductors 
called the armature, designed to revolve in the magnetic field, 
(3) an arrangement of conductors called the commutator for com- 
muting the reversals of the current in the armature into one direc- 
tion in the external circuit, and (4) an arrangement of conductors, 
called brushes, for making connection between the revolving arma- 
ture and the external circuit. 

The magnetic field may be produced by permanent magnets or 
by electromagnets, and in the latter case the current may be taken 
from some external source or from the current produced by the 
revolving armature itself. If the current is taken from the arma- 
ture, all of the current may be used to produce the magnetic field, 
in which case the generator is called a series generator; or only a 
part of the current may be used, the generator then being called a 
shunt generator; or, again, a combination of these two methods may 
be used to energize the field magnets, in which case the generator is 
called a compound generator. 

Separately Excited Generator. 

In this form of generator, the magnetic field is produced by a 
current from a separate source of supply while the current due to 
the induction in the armature is lead off from the brushes to its 
external circuit. A typical form of separately excited generator 
is shown in Fig. 72. 

Series Generator. 

In this form of generator, the magnetic field is produced partly 
by the permanent residual magnetism of the poles, due to the metal 



Generators 



177 



of which they are made, and to the current that is produced as a 
result of the induction in the conductors on the armature. The 
armature conductors are connected in series with the external circuit 
by means of the brushes and the whole current is lead around the 
field pieces. When this current flows around the metal field 
pieces, they become strongly magnetic, producing a strong magnetic 
field in the region in which the armature is made to revolve. The 
stronger the current the greater is the magnetic field, or at least up 
to the point of saturation of the field magnets. By this is meant 




Fig. 72. — Separately Excited Generator. 



the limit in the number of lines of force which the magnetic 
material is capable of producing. The number of times the series 
winding is carried around the field magnet spools, multiplied by 
the number of amperes flowing, is called the ampere turns, and the 
saturation of the magnetic material depends upon a given number 
of ampere turns, beyond which the magnetization will not increase, 
but will rather decrease. 

Fig. 73 shows the typical form of series generator, showing the 
brushes, the field winding, the external circuit, and armature con- 
ductors all connected in series with one another. 



178 



Naval Electricians' Text Book 



In this form of generator, it is seen that no E. M. F. is generated 
in the armature as long as the external circuit is open, for then 
there is no current flowing around the field magnets. There may 
be a small E. M. F. generated due to the residual magnetism, but 
of course is not manifested as the circuit is not complete. In 
order then that this form of generator shall build up, that is pro- 
duce a difference of potential at the brushes, the external circuit 




S/WWW 



Fig. 73. — Series Generator. 



must be completed, and the resistance must not be too high, or the 
small difference of potential, due to the residual magnetism, may 
not be sufficient to force current through it, and thus prevent any 
from flowing around the field magnets. Then, again, a series 
generator will not generate until a certain speed is reached. Any 
increase in the external resistance lessens its power to supply cur- 
rent, lessening as it does its ampere turns and consequently its 
effective magnetism. Any decrease in the external resistance, as 



Generators 



179 



in adding lamps in parallel, has the effect of increasing the current, 
increasing the magnetization, and thus again the current, and a 
continued decrease in resistance might result in burning out the 
armature or the lamps. The series coils must carry the whole cur- 
rent so they must be of large wire to prevent overheating, and of 
only a few turns, for as the proper magnetization is proportional 
to the ampere turns, the latter may be obtained by a large current, 
as in this generator, and a small number of turns. 

Regulation. — The E. M. F. of a series generator may be regu- 
lated at a given speed (1) by controlling the current in the external 
circuit, (2) by cutting out part of the magnetizing coils, and (3) 




Fig. 74. — Series Shunt. 



by sending part of the main current through a shunt to the series 
windings. The only one of these three that finds a practical use 
in the series windings as applied to a compound generator is the 
last and this should be understood, as it is the method used in the 
final compounding of compound generators. 

In Fig. 74, a and b are the terminals for the series windings, 
and in addition to the series winding, these terminals are connected 
by a shunt circuit in which there is a variable resistance c, regulated 
by the short-circuiting plugs d. Part of the main current that 
would otherwise go around the series coils is shunted through this 
circuit, and by moving d the magnetizing current and consequently 
the E. M. F. at the brushes may be regulated. 



180 Naval Electricians' Text Book 

Characteristic Curve. — The characteristic curve of a generator is 
a name given to a curve that may be plotted to show the relation 
between the number of volts generated in a generator and the result- 
ing number of amperes, using volts as ordinates and amperes as 
abscissae. The volts used may be the total volts and the amperes 
the total amperes, in which case the curve is called the total char- 
acteristic curve. In the case of the series generator, if the curve is 
plotted with the E. M. F. at the terminals and the external current, 
also in this case, the internal current, the curve is called the external 
characteristic curve. The m^erwarcharacteristic of a series genera- 
tor would be a straight line, the tangent of the angle this line 
makes with the current line being equal to the internal resistance. 

The curve used in compounding generators is the external char- 
acteristic curve, but as they all show the interior workings of the 
generator under varying conditions a typical curve of each is shown 
with a mention of some of the facts that can be learned from them. 

In Fig. 75 the line OE represents the total characteristic curve 
of a series generator for a given speed, the ordinates being volts and 
the abscissae amperes, being plotted from the total E. M. F. gener- 
ated and the resulting external current. This curve starts a little 
distance above the zero line, showing a certain amount of residual 
magnetism. The curve ascends first at a steep angle, then curves 
around and again assumes nearly a straight course. In this genera- 
tor the magnetization increases with the current, and so the E. M. F. 
increases rapidly at first, giving the straight portion of the curve. 
As the current increases, the magnets approach saturation, so any 
increase in current does not produce a corresponding increase in 
E. M. F. and this is shown by the curving or flattening for a short 
space in the curve. If a still further increase takes place, arma- 
ture reactions, demagnetizing, and cross magnetizing effects take 
place, and a shifting of the brushes due to the increased current 
causes a marked demagnetizing effect and in some generators caus- 
ing a decided drop in the curve. This curve shows at what point 
saturation commences to be manifested, when it has really reached 
the saturation point, and the current necessary to produce the 
maximum E. M. F., or rather the current produced by the 
maximum E. M. F. and at what time the most serious of the arma- 



Generators 



181 



ture reactions take place. It also shows at what current, or the 
limits of current, the total E. M. F. is most nearly constant. 

The curve Oe is plotted for the total current and the difference 
of potential at the brushes or terminals. The difference in the 
ordinates of the total and external characteristics show the volts 
that are lost in overcoming the internal resistance, that of the 
armature and series windings, and from being useless as far as 



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Fig. 75. — Characteristic Curves of Series Generator. 



external electrical energy is concerned are called " lost volts." This 
curve shows between what limits of the external current the 
difference of potential at the terminals is most nearly constant, 
consequently at what load the machine could be used with the least 
variation in E. M. F. 

The full straight line OR is the curve of internal characteristic, 
and its ordinate at any point represents the " lost volts " for the 
corresponding current, and is equal to that current multiplied by 



182 



Naval Electricians' Text Book 



the sum of the armature and series winding resistances. This 
curve then represents the difference between the other two, and 
having either two, the remaining one may be plotted. As the 
internal resistance is known, the internal characteristic may be 
easily plotted, and the data for the external characteristic may be 
obtained by properly connecting an armature in circuit and attach- 
ing a voltmeter to the terminals. Then by adding to the ordinates 
of the external characteristic the ordinates of the internal for the 
same current, the total curve can be plotted. 









OHN19 

Fig. 76. — Curve Showing External Resistance and Terminal Voltage, 

Series Generator. 



Horse-Power Lines. 

Another interesting fact in connection with these curves is that 
they can be made to show the horse-power which is being developed 
at any particular part of the circuit. These horse-power lines con- 
stitute a system of rectangular hyperbolae, the axes of volts and 
amperes being the respective asymptotes. That is xy = a constant, 
x being volts and y amperes. The one horse-power line should be 
the locus of all the points such that the product of the ordinate 
and abscissa? of every point is equal to 746 watts. Thus one point 
would be 74.6 volts and 10 amperes, another 37.3 volts and 20 
amperes, and so on. The two horse-power line should be a result 



Generators 183 

such that the product of ordinate and abscissae at every point should 
be 2 X 746 watts. 

An examination of the resistance curve or line shows that, if the 
resistance is above a certain value, the angle it makes with the 
ampere line being greater than the angle made by the slope of the 
total characteristic curve, the machine cannot build up ; and it also 
shows that while running, if from any cause the resistance is 
suddenly increased, the machine will rapidly unbuild or lose its 
magnetism, that is, the ordinate of the resistance becomes negative 
as applied to the external curve. These curves explain a great 
many things in connection with the running of generators that 
were known before simply as facts. 

Another interesting curve useful in compounding generators is 
a curve showing the relation between the external resistance and 
the difference of potential at the terminals. A typical curve is 
shown in Fig. 76, but its application will be deferred until com- 
pound generators are considered. 

Shunt Generators. 

In this generator, the magnetic field is produced partly by the 
permanent residual magnetism of the field pieces and by a shunt 
current that is led off from the terminals of the machine. As the 
current in the shunt field, as it is called, is lost as far as any 
external electrical energy is concerned, it is sometimes called the 
** lost amperes/' As this loss should be as little as possible, in well- 
designed machines not more than 5 per cent of the armature cur- 
rent passing through the fields, the resistance must be high, and in 
order to produce the proper number of ampere turns, the number 
of turns must be very great, so the shunt winding usually consists 
of a very great number of turns of fine wire. 

Fig. 77 shows the typical form of shunt generator, the shunt 
current being taken off from the brushes around the pole pieces, 
the main current being taken off from the brushes through the 
external resistance R. 

This machine will not build up if the external circuit is closed, 
for then all the current generated would tend to take that path 
on account of its resistance being so much smaller than that of 



184 



Naval Electricians' Text Book 



the shunt windings. If the external circuit is open, and the arma- 
ture made to revolve, owing to the small amount of residual mag- 
netism in the pole pieces, there will be generated a small difference 
of potential at the brushes, and this difference of potential will 
cause a small current in the shunt windings, which will in turn, 
increase the magnetization, this increasing the E. M. F. at the 
brushes, and so the machine gradually builds up to full voltage, 




Fig. 77. — Shunt Generator. 



attaining its full value when no current is flowing in the external 
circuit, and all the armature current is in series with the shunt 
current. When an external current flows due to closing the external 
circuit, the difference of potential at the brushes gradually falls, 
on account of the internal resistance of the armature conductors 
and of the reactions of the current on the field. A greater propor- 
tion of the whole current follows the external path, thereby lower- 
ing the E. M. F. at the brushes, and consequently reducing the 



Generators 185 

shunt current, which decreases the magnetization, and which reacts 
to still lower the E. M. F., so as the external resistance gradually 
falls, the total current may increase for the time, but a less propor- 
tion flows around the field, and the voltage falls, and if a certain 
low external resistance is reached, the machine will rapidly unbuild 
and the voltage and current fall together to zero. 

Regulation. — In order to compensate for the decrease in the E. 
M. F. when load is thrown on a shunt generator, a rheostat of com- 
paratively high resistance is placed in series with the shunt 
winding, and so adjusted that when no external current is flowing 
only enough current flows through the field to produce the proper 
E. M. F., and this is kept constant by throwing out some of the 
resistance as the load increases, so that the shunt circuit will have 
an increasing or rather a steady instead of a decreasing current, 
thereby maintaining a constant magnetization and constant E. M. F. 

Characteristic Curves of Shunt Generators. — There are five curves 
that show relations existing between the volts and amperes in a 
shunt generator, one internal characteristic and four external 
curves. The internal curve, plotted with the total volts and the 
total current when the external circuit is open is very similar to 
the total characteristic curve of the series generator. When the 
external circuit is closed, there are four variable quantities, namely, 
the total E. M. F., the E. M. F. at the brushes or terminals, the 
armature or total current, and the external current. Calling the 
total E. M. F. E, the E. M. F. at the terminals e, the total current 
Ca, and the external circuit C, four curves can be plotted, e and C, 
e and Ca, E and C, E and Ca. Of these e and C is the one prin- 
cipally concerned in the compounding of generators, though all are 
of interest and are shown in Fig. 78. 

Curve Xo. 1 is plotted from e and C, No. 2 from e and Ca, Xo. 3 
from E and C, and Xo. 4 from E and Ca. OA is drawn at such 
a slope that the tangent of the angle it makes with the ampere 
axis represents the resistance of the armature, and OS at such a 
slope that the tangent of its angle represents the resistance of the 
shunt winding. 

If curve 4, obtained with the total E. M. F. and the total cur- 
rent, is plotted, the others may all be obtained from it. Curve 2 



186 



Naval Electricians' Text Book 



is obtained from 4, by subtracting from the ordinates lengths 
which are included between OA and OC. Thus the point 2 is 
obtained by subtracting the distance CF from (74. The distance 
CF represents the " lost volts " for the current OC corresponding 
to the E. M. F. (74, and similarly the ordinates represent the lost 
volts for any corresponding armature current. 

Curve 3 is obtained from 4 by subtracting the abscissae lengths 
which are included between 08 and OD. Thus the point 3 is 
obtained by subtracting the distance DE from ZM. The distance 




o 
Fig. 78 



AMPERES 

-Characteristic Curves of a Shunt Generator. 



DE represents the amperes in the shunt circuits, or the " lost 
amperes" for the difference of potential (74, and similarly the 
abscissae between OS and OD represent the lost amperes for any 
corresponding difference of potential. 

Curve 1 is obtained by taking the ordinates (lost volts) from 
curve 3 and the abscissae (lost amperes) from curve 2 correspond- 
ing to any point on curve 4. 

In practice, it is more usual to plot curve 1, by observing the 
difference of potential at the terminals with a voltmeter and 
measuring the external current with an ammeter. Curves 2 and 
3 can then be drawn, and from these two, curve 4 can be plotted. 



Generators 



187 



These four curves are curiously different from that of the series 
generator. The volts are a maximum when the external circuit is 
open, and as the external current gradually increases, the difference 
of potential gradually falls, due to the fact that a smaller propor- 
tion of the total current is now flowing around the field magnets. 
At first this fall is gradual, but at a certain current the curve rapidly 
turns and then descends rapidly towards the origin in a nearly 
straight line. This shows why a shunt generator will not build up 
if the external circuit is closed, and how it rapidly unbuilds if the 
external resistance is lowered to a certain amount. The straight 
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Fig. 79. — Curve Showing External Resistance and Terminal Voltage, 

Shunt Generator. 



portion shows the critical state, and shows that if the external 
resistance is altered the slightest degree, both the volts and amperes 
alter to a very great degree. 

These curves show that the shunt generator will only work if the 
resistance of the external circuit is greater than a certain value, 
while the series generator will only work if the resistance is less 
than a certain value. 

A curve (Fig. 79) showing the relation between the volts and 
resistance is instructive, as by its combination with the corre- 
sponding curve of the series generator the curve for the compound 
generator is made. 



188 



Naval Electricians' Text Book 



Compound Generators. 

Having now seen the principles upon which the series and shunt 
generators are built, we are in a position to take up the compound 
generator, which is simply a combination designed to produce a 
constant difference of potential at the terminals irrespective of the 
external current or resistance. A compound generator can then 
best be considered as a shunt generator, upon which there is also 
wound a few turns of series windings. Under the curve for the 
shunt generator it was seen that as the external current was in- 
creased, or what amounts to the same thing the external resistance 




ohms 
Fig. 80. — Curve of Compound Generator. 



decreased, the difference of potential gradually fell and in the series 
curve, the difference of potential gradually increased under the 
same circumstances. So by combining these two curves, a curve 
of constant potential or a straight line might be produced, and 
that is the sole object of the compound generator. This could be 
well represented by combining the two external curves of the series 
and shunt generators, but is still better shown by combining the 
two curves plotted with volts and ohms, for each generator as 
shown under the respective heads of series and shunt generators. 
These curves are shown in the figure. 

The shunt curve in Fig. 80 shows what was seen before, that the 
greatest E. M. F. occurs when the external resistance is greatest, 



Gexerators 189 

or when the external circuit is open, and as the resistance is gradu- 
ally decreased, or the external current gradually increased the 
E. M. F. gradually fell. The opposite takes place in the series 
generator, for when the resistance is high scarcely any current 
flows around the field spools, and there is practically no E. M. F., 
but as the resistances decreases, or current increases, the E. M. F. 
gradually rises. If there is a proper relation between the resist- 
ances of the two windings, one will raise the E. M. F. just as much 
as the other lowers, so the sum of their ordinates at any point will 
be constant, and the compound characteristic is represented by the 
dotted straight line, marked compound. 

In the type of compound generator used in the navy, in addition 
to the fixed shunt and series windings, there is a regulator intro- 
duced in the shunt field as explained under the shunt generator, 
and a shunt to the series winding as explained under the series 
generator. This latter is adjusted when the machine is being com- 
pounded, and when once adjusted to give the proper difference of 
potential should not thereafter be tampered with, but any varia- 
tions in the E. M. F. should be regulated by the shunt field rheostat. 

The Building Up of a Generator at Starting. 

When a self -excited generator is started, there is a small E. M. F. 
induced in the armature coils due to the magnetic field produced by 
the small residual magnetism. This small E. M. F. produces a 
current which, flowing around the magnets, strengthens the field, 
which in turn induces higher E. M. F. ; this produces greater cur- 
rent which still more strengthens the field and so on until the ma- 
chine is built up to full voltage. This operation is called building 
up, and there can be no building up unless there is some residual 
magnetism. If the field magnets show no residual magnetism 
whatever, the field circuit should be connected with some outside 
source of current, either a few cells of a storage battery or the cur- 
rent from a running machine. 

If the connections of the field are such that the induced current 
tends to weaken the residual magnetism, then the machine cannot 
build up at all. With a given direction of rotation of the armature 
and a certain polarity, the induced current tends to go in a certain 



190 Naval Electricians' Text Book 

direction. If now the connections are such that the induced cur- 
rent due to the residual magnetism weakens it, the current will 
also weaken. If the current was strong enough to reverse the 
polarity of the field magnets, then the induced currents would flow 
in the opposite direction and would be again acting to weaken 
the field. 

With a given direction of armature rotation and given field con- 
nection, a generator does build up ; it cannot build up, if its direc- 
tion of rotation be reversed, or if its field connection is reversed; 
but it will build up, however, if both the direction of rotation and 
field connections are reversed at the same time. 

If a generator does not build up, it may do so by changing either 
the direction of rotation of the armature or by changing the field 
connections. 

Comparison of Terminal Voltage in Different Generators. 

The field current of a separately excited generator can be kept 
constant, so that the armature flux is practically constant except for 
the demagnetizing effect of the armature when delivering its 
current. 

Separately Excited Generator. — As the current rises, due to a 
lessening of the external resistance, the drop of potential in the 
armature, C a r a , increases, so the terminal voltage decreases with 
an increase of current, and also slightly due to the increased de- 
magnetizing effect when the current increases. 

The terminal voltage falls off as the speed decreases, as the total 
E. M. F. depends on the speed and flux, as seen from the funda- 
mental equation, and the total and terminal voltages vary almost 
in proportion with the speed. 

Series Generator. — The total E. M. E. is proportional to the 
speed and for any given external current, the terminal voltage 
varies directly with the total E. M. F. and with the speed. 

The voltage is zero when the current is zero and increases rapidly 
with the external current, the lost volts increasing with increase 
of current. With a certain speed, the terminal voltage falls off 
as the external resistance is decreased. 

Shunt Generator. — A decrease of speed in a shunt generator 



Generators 191 

causes a decrease in both the total and terminal voltages, and the 
lessening of the terminal voltage decreases the field current and 
consequently the magnetism, so the voltages fall more in proportion 
than in a separately excited machine. 

An increase in the external current causes a greater decrease in 
the terminal voltage than in a separately excited generator, because 
on account of the increased armature current, the drop is greater, 
and consequently the terminal voltage is less, and also the field 
excitation is less. 

Compound Generator. — The field excitation of a compound gen- 
erator is increased by an increase in the external current due to 
the series windings. If the series winding has enough coils, it may 
counterbalance the demagnetizing action due to the increased cur- 
rent and the drop in the terminal voltage due to the shunt winding 
and may increase the total E. M. F. 

If the series coils are made of just enough turns to counteract 
the drop in the armature and field due to the increased current, 
C a r a + C a r m , the terminal voltage may be kept approximately 
constant. 

If the series windings has the effect of increasing the total 
E. M. F., that is, if it more than compensates for the drop, the 
terminal voltage will increase with increase of current, and the 
machine is said to be over compounded. 

Over Compounding. 

By proper adjustment of speed and resistances, machines can be 
made to give a constant difference of potential for a certain range 
of external current which may not be constant over the entire limit 
of external current. A machine is said to be over compounded 
when the difference of potential at the terminals is higher than 
the E. M. F. at some point in the circuit over which the E. M. F. 
is to be constant for the range of current used. It is usually due 
to a preponderance of the series winding over the shunt. There 
is no necessity of over compounding generators on board ship for 
the leads are short and their resistances low. It is, however, abso- 
lutely essential to know over just what range of external current 
the E. M. F. is constant. Thus, of two machines built entirely 



192 Naval Electricians' Text Book 

alike of 100-amperes capacity, one might have an absolutely con- 
stant E. M. F. from to 50 amperes, and not so constant for the 
rest of the load, while the other might be not quite so constant in 
the first half of its range, but entirely constant in its second half. 
In running these machines in parallel, they would only automatic- 
ally work so to speak, over the range of current common to both in 
which the E. M. F. was constant, though of course they could be 
regulated so as to divide their loads equally by adjusting the shunt 
rheostats. 

Uses of Different Classes of Generators. 

Separately excited generators are used mostly for testing where 
a constant E. M. F. is desired or where changes of speed affect but 
slightly the terminal voltage. 

Generators used for charging storage batteries are usually sepa- 
rately excited, as they are working against an opposing E. M. F. 
which would act back through the generator if it was not imme- 
diately disconnected on stopping. Separately excited generators 
are much less likely to have the field magnetism reversed. They are 
also used largely for electroplating. 

Series generators cannot be used where constant voltage is de- 
sired, but can be used for supplying constant current at varying 
voltages, the voltage being regulated by devices to keep the current 
constant on changes of the external resistance. 

Shunt or compound generators are used for delivering varying 
current at constant voltage, as in electric lighting and in most 
forms of power. They are driven at or near constant speed by the 
motive power available. 

The fields of alternating current generators are separately excited, 
as a steady field could not be produced by the alternating current 
of the armature. 



CHAPTER XI. 

EFFICIENCIES AND LOSSES OF GENERATORS. 

Efficiency as applied to a generating set, that is, a generator and 
the power that drives it, is a term used in more than one sense, 
and to intelligently understand what is meant, the definitions of 
the terms ordinarily used will be given, and reasons given for the 
existing differences. 

Gross Efficiency. 

On board ship, the generators are directly connected to the shaft 
of the driving engine, either by means of a solid shaft or by a 
clutch bearing. All of the power developed by the engine and 
applied to the armature is not converted into electrical energy in 
the generator, and the gross efficiency is a term applied to express 
the relation between the gross power actually applied to the arma- 
ture shaft and the gross electrical power converted in the armature. 
One of these is mechanical power, the other electrical, and to obtain 
the percentage efficiency, they must both be expressed in the same 
units, either both electrical or both mechanical. 

The total power applied to the shaft is ordinarily obtained by 
taking indicator cards of the engine while running at the standard 
speed. The total electrical power converted can best be determined 
by calculation; by measuring the total external current and the' 
difference of potential at the terminals, and from these quantities, 
by means of the dynamo equations, find the total E. M. F. and the 
armature current. Their product divided by 746 will give the 
horse-power actually converted, and the percentage of the total 
horse-power that this represents will be the gross efficiency. It must 
be noted that in expressing the gross efficiency, it is necessary to 
state under what conditions of external load the generator is run- 
ning, for the total power converted depends upon this quantity and 
hence does the efficiency. 



194 Naval Electricians' Text Book 

Electrical Efficiency. 

This is a term given to express the relation between quantities 
that are entirely electrical, and might be considered the efficiency 
of the generator itself. It is the relation between the total power 
actually converted in the generator and the net output, or the electri- 
cal energy available at the terminals. The output is measured by a 
voltmeter and ammeter properly connected with the generator run- 
ning at its rated speed, and with the load for which the efficiency is 
desired. With these quantities the total E. M. F. and the total 
armature current are obtained as in the case under gross efficiency. 
The product of the total E. M. F. and armature current gives the 
total number of watts converted, and the product of the difference 
of potential at the terminals and the external current gives the 
number of watts available for useful work, and the relation between 
these two quantities expresses the electrical efficiency. 

Commercial Efficiency. 

This is a term given to express the relation between the total 
power applied to the shaft of the generator and the total electrical 
energy available at the terminals, and as has been seen, must be 
the product of the other two efficiencies, the gross and electrical. 
This is the real measure of the efficiency of the generating set, and 
represents the relation between the power that is put in the set, 
the input, and the power that is taken out, the output. If the other 
two efficiencies are high, of course the commercial efficiency will be 
high also, though lower than either one. The quantities concerned 
.are directly measured, one by the indicator cards of the engine, the 
other by voltmeter and ammeter ; and the resulting efficiency is the 
one required by the standard specifications, full load on the genera- 
tor being the standard load. 

Losses. 

Losses in generators are of two kinds, electrical and mechanical, 
and on their values depend the various efficiencies. The losses 
which represent the difference between the total power applied to 
the armature shaft and the total power converted in the armature 



Efficiencies axd Losses of Generators 195 

are partly mechanical and partly electrical, being losses in friction 
at the bearings, friction at the brushes, between them and the 
commutator, air friction of the revolving armature, eddy currents 
in the pole pieces of the magnetic field and in the conductors on 
the armature, and in the armature core, and a hysteresis loss in the 
armature core due to the armature revolving in a magnetic field. 
All of these losses are manifested in the form of heat which is 
dissipated into the air or tends to heat the parts involved and, being 
brought into existence by the power supplied, represents so much 
waste energy. 

Of these losses, the friction losses are small and can be reduced 
by proper mechanical means. The loss due to the eddy currents 
induced in the pole pieces is also small, especially in forms of 
armature that are not slotted. These eddy currents are induced in 
and circulate round the pole pieces, being due to the relative motion 
of the lines of force and the iron masses, the field being apparently 
dragged along by the revolving armature, and the magnetic circuit 
being broken as the tip of the pole is left. These eddy currents 
can be reduced to a certain extent by laminating the pole pieces, 
and by increasing the size of the pole tip on the leaving horn of 
the pole piece, and cutting it away under the entering horn; the 
last arrangement also reducing the demagnetizing and cross mag- 
netizing effect. The eddy currents tend to heat the iron masses, 
and this heat represents so much lost energy. 

Loss due to eddy currents set up in the armature conductors 
themselves is very small indeed and could only be appreciable, if 
at all, in armatures having heavy solid bars as conductors, but 
could have no effect in armatures where the conductors are made 
up of stranded small wires. 

The principal loss in power that is not converted into electrical 
energy in the armature is that due to hysteresis which is due to the 
reversals of the magnetic field and its reaction on the iron masses 
of the armature core. Hysteresis is the name given to express the 
magnetic lagging of effects behind the causes which produce them. 
If the magnetism be rapidly reversed in a magnetic substance, there 
is a lagging of the field behind the cause of the reversal and to 
this phenomenon the name hysteresis has been given. The rapid 



196 Naval Electricians' Text Book 

reversal of a magnetic field will produce heat in the magnetic sub- 
stance, which is a loss from the power which produces the change. 
The revolution of the generator armature in a magnetic field has 
the effect of reversing the magnetic field ; the same effect, in fact, 
as though the armature was at rest and the field was actually 
reversed. Laminating the iron core of the armature has the effect 
of reducing eddy currents and a consequent loss due to heat they 
produce, but it does not affect the hysteresis loss, as that depends 
only on the magnetic substance of the core, on the flux density of 
the magnetic field, and on the number of reversals of the field; this 
last depending on the speed and number of poles. 

The loss due to hysteresis is reduced by using as armature discs 
soft annealed metal that does not show much residual magnetism, 
and this is effected by using a metal approaching pure iron, having 
little of the steel characteristics. 

The loss in armatures due to eddy currents and hysteresis may 
be separated, as the eddy currents are true electrical currents, and 
their heat waste varies as the square of the current, and the hyster- 
esis loss only as the current. 

The difference between the power actually converted in the 
armature and the electrical output of the generator is represented 
by the losses which take place in the conductors of the generator 
itself; that is, in the armature conductors and in the conductors 
that make up the series and shunt windings. The losses in the 
windings of the field are designated field losses, and those in the 
armature, armature losses, to distinguish them from the losses in 
the armature core, which are sometimes called core losses. 

In a compound generator there are two field losses, that due to 
the series windings and that due to the shunt windings. When 
the generator is giving out its rated E. M. F., the shunt loss is 
constant as the current is constant to produce the constant mag- 
netization, and the resistance being unchanged. The loss then ex- 
pressed in joules would be C 2 s r s t. It must be borne in mind, how- 
ever, that if there is a regulator in series with the shunt field, loss 
due to its resistance must be added to the other, in joules being 
C 2 s rt (regulator). The loss in the series windings depends on the 
external load, the series current varying with the armature current 






Efficiencies axd Losses of Generators 197 

at any time, its loss in joules being C 2 m r m t. The armature loss 
depends on the external load, and at any time would be C 2 a r a t joules. 
All these expressions show that the smaller the resistances, the 
smaller the losses — and the ideal generator would be one of infi- 
nitely small resistance. These are all heat losses, the effect of 
which is to heat the conductors through which the currents flow, 
and unless some means is taken to allow the heat formed to be 
radiated off, this heat forms a serious drawback, independent of the 
loss of electrical energy. The series coils are usually in the form 
of ribbon, for the double purpose of allowing greater radiating sur- 
face and for the ease with which they can be wound on the magnet 
spools. 

These losses can be considered in another sense, that of the 
power used to force the currents through the several resistances. 
For instance, in the case of a long-shunt compound-wound gener- 
ator, the difference of potential at the terminals being e, the power 
in watts expended in forcing the current through the shunt winding 
would be eC s • That lost in forcing the current through the 
series windings would be (e f — e)C m , and that lost in the arma- 
ture (E — e')C. 

From the dynamo equations, Chapter XII, 

e = C s ?' s , 

or eC s = C 2 s r s 

6 6 — C al'm 

y6 6 ) C m — — (- J ~m1'm • 

In the long shunt 

^a —— C'wi 

and (E — e')=C a r a 

(E — e')C a =C 2 a r a . 

Multiplying these by t, expresses the watts lost as joules. 

The total power converted in the armature is the product of 
the total E. M. F. and the total armature current or EC a ; the total 
available power is the product of the difference of potential at the 
terminals and the total external current or eC. The difference of 
these two must represent the total copper losses, or in the long 
shunt compound generator, 

EC a — eC = C 2 s r s + C 2 a r m + C\r a . 



198 Naval Electricians' Text Book 

The total available power in the external circuit is C 2 R, or 
EC a = C 2 R + C 2 s r s + C\r m + C\r a . 
eC = C 2 R, 

which is, of course true as 

e = CR. 

The expression for the electrical efficiency would be 

eC 
Efficiency = j^q ; 

or, as given under dynamo equations, 

™ . _ C 2 R 

i^mciency _ C2R + c% ^ + ^^ + Q2 ^ . 

Limit of Output. 

In the case of a generator designed to give a constant difference 
of potential at the terminals, the amount of current flowing through 
the armature depends on the external resistance. As this resistance 
is reduced by adding incandescent lamps in parallel, it becomes a 
matter of importance to know how far this resistance may be low- 
ered; or, in other words, how much current can be safely taken 
from the generator. In a given generator the calculations are 
based on a given maximum current, and the conductors of the arma- 
ture are calculated to safely withstand this current; but the ques- 
tion is, what limits the current and what should be the basis of the 
calculation? We have seen under losses that the internal losses in 
the generator are all in the nature of heat losses, the number of 
joules lost in a given time being C 2 rt, for the part of the circuit 
under consideration. 

Heat. — The heat formed by the currents tends to dissipate itself 
into the surrounding air, but if the heat is produced by the current 
faster than it is radiated, it is very evident that the parts themselves 
will be heated. If the generator is at rest and has been for some 
time, all of its parts will attain the temperature of the air; if now 
the generator is started with an external current, heat is formed in 
the conductors, and if it is radiated as fast as produced there will be 
no rise in temperature. This is seldom the case, however, and the 



Efficiencies and Losses of Generators 199 

temperature of the parts will go on slowly rising. The greater the 
current taken from the generator, the greater will be the increase 
in temperature for the same time. Now it is very evident that one 
limit of the amount of current is the temperature limit due to 
that current. At a certain temperature the materials used in the 
insulation of the conductors and the different windings of the 
generator, such as paper, cotton, silk, etc., will char and disintegrate 
to such an extent as to be worthless for what they were designed. 
For a short time they may stand a temperature somewhat higher 
than the charring temperature, but if submitted for any length of 
time to a temperature of 180° F., they will quickly break down. 
Consequently, no current should ever be taken from a generator 
such that the heat formed should raise its temperature to 180° F. 

If the temperature of the air is as high as 180° F., it is very 
evident that the machine should not be run at all, for all parts 
will be at that temperature, and there could be no allowable rise 
in temperature, due to the generator currents, so in stating the 
allowable rise, it is very necessary that it should be a rise in tem- 
perature above that of the surrounding air. If the machine could 
be kept- in a room at the freezing point, and the heat imparted to 
the air so carried away that it would remain at the freezing point, 
the allowable rise due to the current would be 180° — 32°, and 
from this generator under those conditions, a greater current could 
be safely carried than at any initial higher temperature. 

The specifications for generators used in the service state that 
after a four-hours' full-load trial, no part of the machine shall 
be allowed to be higher than 40° C, greater than the temperature 
of the room ; or, in other words, the temperature due to the arma- 
ture current shall not be greater than 40° C, above the temperature 
of the air. The average temperature of the air is to be taken as 
25° C. 

Sparking. — Besides the limit of temperature which limits the 
amount of current that can be safely carried, there is another con- 
sideration that will be lightly touched on. As the current from the 
armature increases, the magnetic field of the armature core increases 
and the magnetic field of the field pieces remaining constant, cer- 
tain reactions take place between these two fields. These reactions 



200 Naval Electricians' Text Book 

have a tendency both to cross magnetize and to demagnetize, one 
effect of which is to necessitate the shifting ahead of the brushes 
from their normal positions. The brushes should ordinarily be 
placed in the neutral part of the field, that is, where the induction 
in the armature coils is a minimum, and in this position there will 
be little or no sparking. If the current is increased, greater reac- 
tions take place, necessitating further movement of the brushes to 
reduce sparking, but this movement of the brushes produces further 
change in the magnetic reactions, and if the current is strong 
enough the armature field may be powerful enough to overcome the 
field, and there can be no position found in which the brushes will 
have no sparking. This sparking of course is very injurious, and 
when heavy, rapidly wears away the brushes and the commutator 
segments, rapidly pitting and scarring them, and the heat due to 
the sparking may be great enough to fuse two or more adjacent 
segments, thereby short-circuiting their coils, and soon burning 
them out. This sparking can be reduced by good preliminary de- 
sign ; by making the field magnets relatively very powerful in rela- 
tion to the armature field, but still in any given generator, a current 
in excess of the designed amount may produce injurious sparking, 
so this may well limit the amount of current that may safely be 
taken from any machine. 



CHAPTER XII. 
DYNAMO EQUATIONS. 

In order to know just what is taking place in a generator when 
it is running at any certain speed with a given load in the external 
circuit, the dynamo tender should have a knowledge of the simple 
equations connecting the electromotive forces, currents, and resist- 
ances of the various parts of the field windings, armature, and 
external circuit. These follow directly from a consideration of 
Ohm's law and the laws of divided circuits previously given. These 
equations will enable one to calculate just what any particular 
generator is capable of doing, and are needed in order that the 
several efficiencies may be calculated under any given conditions. 
Of course they are used when the generator is under design, but 
with which this is not concerned. Examples will later be given to 
show their application. 

The following notation will be used consistently throughout 
both with generators now and motors later : 

E = total E. M. F. generated by generator or motor ^ 
e = difference of potential at the terminals, 

e' = difference of potential at the brushes, 

(2 = difference of potential at the motor terminals, 
C a = armature current, 
C s — shunt current, 
C m = series current, 

C = external current, 

r a = armature resistance, 

r s = shunt resistance, 
r m = series resistance, 

R = external resistance. 



202 



Naval Electricians' Text Book 



Series Generator. 

In the series generator, there is but one circuit (Fig. 81), so 

G =z L>a —— ^m • 




Fig. 81. — Series Connections. 

By Ohm's law : 
The fall of potential around the whole circuit E = C(R -\- r a + r m ), 
" " " from terminal to terminal e = CR, 

" " brush to brush e' = C(R + r m ), 

" " through series windings e' — e = Cr m , 

armature E — e'= Cr n . 

Useful work in external circuit = Cet = C 2 Rt joules. 

Total work in circuit = CE =C 2 (R+r a +r m ) £ joules. 

Useful work C 2 Rt e 

Electrical efficiency = Total work = CHR+r a +r m )t = E ' 

The expression for efficiency shows that it is a maximum when 
both r a and r m are very small. 



hAAAAAA 




Fig. 82. — Shunt Connections. 



Dyxamo Equations 



203 



Shunt Generator. 

In the shunt generator (Fig. 82) there are three currents, one 
through the shunt windings, one through the external circuit, and 
one through the armature, the latter being equal to the sum of the 
other two. In this case the terminals and brushes coincide. 

Rr 8 



Total resistance outside of armature = 



R + r, 



The fall of potential around the whole circuit E = C a [ r a + 



Rr f 



R + r s 



)> 



from terminal to terminal e = CR, 
from terminal to terminal e = C s r s , 
through armature E — e= C a r a , 
(C + C s ) r a 



C =H 



e + 



e e 

R +7: 



_ o (R r s +Rr a + r a r s 
Rr s 



or 



E = er a 



1 _1_ 1 

R + r a + T~ s 

an expression which allows E to be computed, by the several resist- 
ances being known and e measured at the brushes by a voltmeter. 

Useful work in external circuit = C-Rt joules, 
Work spent in shunt field = C 2 s r s t 

Work spent in armature = (P a r a t 

or 



Electrical efficiency 

(VWW 



G-R 



CR + CVs + CTaTa 




Fig. 83. — Short Shunt Compound Connections. 



204 



Naval Electricians' Text Book 



Compound Generator. 

There are two cases in the compound generator, depending on 
whether the shunt current shunts only the brushes as shown in 
Fig. 83, or shunts both the armature and series windings as shown 
in Fig. 84. The former is called a short shunt compound gen- 
erator and the latter a long shunt compound wound. 

^6 




Fig. 84. — Long Shunt Compound Connections. 



Short Shunt. 

I ' {R -A-T ) f \ 
The fall of potential around the whole circuit E—G a [ r a -f- p _Ty m , * , 

v -tv -\- r m -f- i s i 

" from brush to brush e' = C s r s , 

" from brush to brush e? = Gr m + CR, 

" " terminal to terminal e = CR, 

" through armature E — e' = G a r a , 

" through series windings e' — e = Cr m . 

Lost volts E — e = C a r a + Cr m . 



From the above expressions follows an equation by which the 
total E. M. F. may be calculated, knowing by measurement the 
difference of potential at the terminals and the value of the several 
resistances. 

e(r m r„ + Rr s + r a r. 9 + r a r m + Rr„) 



E 

Useful work in external circuit = C 2 Rt joules, 
Work spent in shunt field = C 2 s r s t " 

" " series " = (Pr m t " 

" " " armature = (PaTat 

or 

G 2 R 



Rr, 



Electrical efficiency 



(PR + CVs + C 2 r m + C\r a 



Dynamo Equations 205 

Long Shunt. 
The fall of potential around the whole circuit E = C a \r a + r m 

from brush to brush e' = C a r m + CR, 

from terminal to terminal e — CR, 
" » " from terminal to terminal e = C s r s , 
through armature E — e'= C a r a , 
" " series windings e' — e = G a r m . 

Lost volts E — e = C a r a + C a r m . 

A similar expression, as in the case of the short shnnt com- 
pound, may be deduced, 

E = e(r m r s + Rr s -f r a r s + Rr m + Rr a ) 
Rr s 

the only difference being in the next to the last term. 

Useful work in external circuit = C 2 Rt joules, 

Work spent in shunt field = C 2 s r s t 

" " series " = C 2 a r m t 

" " armature = C 2 ^^ " 



or 



Electrical efficiency 



G 2 R 



CrR ~r C $ r s T~ C' a T m i C"a r a 

Problems on Generators. 
1. If a shunt wound generator has an E. M. F. of 108 volts at the 
terminals, resistance of armature .05 ohm, field coil 18 ohms, and out- 
side mains .2 ohm, how many incandescent lamps can be lighted if 
each takes .75 ampere and nas a hot resistance of 130 ohms? Find 
the total electrical energy and the energy in the lamp circuit in watts. 
If the net efficiency is 82 per cent, how many H. P. must be applied to 
the armature? 

* = No. of lamps C — ~ — — 1^__ C= .75z, 

E = e + C a r a C a = C + C s c s = ^-i^=6 

C a = .75 X 70 + 6 = 58.5. 
E = 108 + 58.5 X .05 = 110.93 volts. 

Total electrical energy = EC a = 110.93 X 58.5 = 6489.5 watts. 
Total electrical energy in lamp circuit 

= eC = 108 X 52.5 = 5670.0 watts 

Net eff - *°— - ^or H.P. = B670_X100 = 9 26 

wet en, — H.P. X 746 — 100 82X746 S, ^ D * 



206 Naval Electricians' Text Book 

2. In a shunt generator, the resistance of the armature is .02 ohm; 
of the shunt field 20 ohms; of the lamps and mains .4 ohm; voltage 
at terminals 80. Find the total current, lost volts, percentage of loss 
in the armature and in the field magnets, and the current through the 
shunt field. 

80 

e = C s r s or G s == -^ = 4 amperes, 

80 
e = GR orC=-|- = 200 

C a = C + G s = 200 -f- 4 = 204 amperes. 
Lost volts = G a r a = 204 X .02 = 4.08 volts, 
E = e + lost volts = 84.08 volts. 

fo loss in armature =- 84 Qg = 4.8$. 

Watts lost in field = eC s = 80 X 4 = 320 watts. 

Total watts r=.EC = 84.08 X 204. 

320 
% loss in field = 84>Q8 x 2Q4 = 1.8*. 

3. In a given generator, the loss in the armature is 1000 watts, in 
the field magnets 600 watts, hysteresis and other losses 280 watts, loss 
in engine 5920 watts. If 57,800 watts are supplied to the engine, how 
many 16 c. p. lamps at 4 watts per c. p. can be lighted? What is the 
commercial efficiency of the plant? 

Ans. No. of lamps 781. 

Commercial efficiency 86.5 per cent. 

4. A shunt generator, total E. M. P. 100 volts, resistance of field 16 
ohms, of armature .12 ohm, of external mains .2 ohm. How many 
lamps taking .8 ampere and having a hot resistance of 100 ohms will 
this generator maintain? 

If 9% H. P. is applied to armature shaft, what is the gross and net 
efficiency, and energy in watts lost in field and in armature? 

# = No. lamps e = E — C a r a = C s r s = CR, 



B = .2+^ CR=E—iC+C 8 )r a = E — (c + 2!?y ai 

8 
Rr a = Er s G = yq x 

16 X (500 + x) 8000 + 16a? 



8 
or CRr s + Cr a r s +CRr a = Er s G = rr 



192 

rdT, = .12Xl6= I50 

_ 12 500 -f x _ 6000 + 12a; 
RTa — 100 X bx — 500^ 



8 /8000+16x , 192 6000+ 12x\ _ '„ 
Ton 55T— + 1TO+ 600s j = 10Q Xl6 

x = 75 + , 



Dyxa^io Equations 207 



e = CR = 60 X 1.532 = 91.92 = ff g r s . .*. C s = 5.745 
G a = C +C= 65.745. 
Total energy = #C a = 100 X 65.745 = 6574.5 watts = 8.813 H.P. 
Useful energy = eC =91.92 X 60 = 5515.2 watts = 7.342 H.P. 

Gross eff . = ^? = 92.77# Net eff . = ^i? = 77.81 %. 



Energy lost in armature = C 2 a r a = 65.745 X .12 = 518.7 watts, 
Energy lost in field = C 2 s r s = 5.745 2 X 16 = 528.08, 

Energy in lamp circuit = (PR = ~60 2 X 1.532 = 5515.20 
or total energy 6561.98 watts. 

5. A long shunt compound wound generator, working with 3.6 ohms 

in the regulator, is furnishing a current in the external circuit of 117 

amperes with a difference of potential at the terminals of 108 volts. 

The resistance of the shunt is 32.4 ohms, of the series field .015 ohm, 

and of the armature .045 ohm. Calculate the lost volts, current in 

armature, current in the field coils and the efficiencies, the power 

applied at the shaft being 20 H. P. 

108 
e = C s r s or C s = 32 4 ■ 3 6 — 3 amperes, 

C a = C + C s = 117 + 3 = 120 amperes, 
.. Lost volts = C a ( r a + r m )= 120 ( .045 + .015 ) = 7.2 volts. 
Total watts developed = EC a = (108 + 7.2) X 120 = 13824 
utilized = eC = 108 X 117 = 12636 

supplied = 20 X 746 = 14920 

Gross eff. = i|||^ = 92.65^.* Elec. eff. = *§||| = 91.4*. 

Net eff. = ^^-=84.69*. 

6. A compound wound long shunt generator, resistance of armature 
.023 ohm, of series field .012 ohm and of shunt 20 ohms, maintains 300 
110 volt 20 c. p. lamps, each lamp requiring 4 watts per c. p. Find 
the total E. M. F. of the machine. Allowing 15 per cent for friction 
and other losses, find the H. P. of the engine required to run the 
generator. 

Watts in external circuit = 300 X 20 X 4 = 24000 

24000 mn-,0 • * , • -x 

Q = 218.18 amperes in external circuit. 

C s r s = 110 C s =:^ = 5.5, 

C a = C+C s = 218.18 + 5.5 = 223.68 , 

E = e + C a (r a +r m ) =110 + 223.68 X (.023 + .012) =117.8 volts. 

TT „ . . EC a 117.8X223.68 .. _- 

H.P. required = 746 x , 85 = - 7 46 x . 85 = 4L55 ' 



208 Xaval Electricians' Text Book 

7. A compound wound generator, long shunt, maintains a difference 
of potential between the mains of the external circuit of 80 volts. 260 
incandescent lamps of 16 c. p. each are placed in multiple arc between 
the mains, each lamp requiring 4 watts per c. p. The resistance of the 
armature is .02 ohm, series coils .005 ohm, and shunt current is 7 
amperes. Find the gross, net, and electrical efficiencies when 26 H. P. 
is applied to the shaft of the generator. 

Arts. Gross eft = 94.61 $. 
Elec. eff. = 90.65$. 
Net eff., = 85.77$. 

8. A long shunt compound wound generator maintains a difference 
of potential of 80 volts between the mains of the external circuit. 250 
incandescent 16 c. p. are placed in parallel on the mains and each lamp 
consumes 4 watts per c. p. Resistance of armature = .0177 ohm, of 
series coil = .005 ohm. Shunt current = 7 amperes. Find the gross, 
net, and electrical efficiencies when 25 H. P. is applied to dynamo shaft. 

Ans. Gross eff. = 94$. 
Elec. eff. = 91$. 
Net eff. =86$. 

9. The machine in the preceding example develops a total E. M. F. 
of 83 volts; find the number of 16 c. p. lamps, resistance 100 ohms, 
placed in parallel that it will maintain, allowing 4 watts per c. p. 
Resistance of shunt = 5.8 ohms. 

Ans. 148 lamps. 

10. A current of 10 amperes is sent through a series of 10 arc lamps, 
each of 3.8 ohms resistance, by a generator whose armature is making 
1000 revs, a minute. The arc lamps are then replaced by 8 incandes- 
cent lamps, each of 120 ohms resistance and arranged in 4 series of 2 
each; the armature is then made to turn at 1044 revs, per minute. The 
resistance of the generator is 3 ohms. Assuming that the E. M. F. de- 
veloped is proportional to the speed; find the strength of current in 
each lamp. Ans. 1.7 amperes. 

11. A given shunt generator gives a total E. M. F. of 100 volts when 
run at a speed of 1000 revs, per minute. The shunt resistance is 50 
ohms. What total E. M. F. will this generator induce if run at a speed 
of 1500 revs, per minute, if the shunt field is kept constant? What will 
have to be the resistance of the shunt to keep the field constant? Neg- 
lect the resistance of the armature. Ans. E. M. F. 150 volts. 

Resist. 75 ohms. 

12. The total E. M. F. of a shunt generator decreases from 125 volts 
to 100 volts when the speed is reduced from 1200 to 1000 revs, per 
minute. The armature flux at the higher speed is 10,000,000 lines. (1) 
What is the armature flux at the lower speed? (2) What would be the 



Dynamo Equations 209 

E. M. P. of the generator at the lower speed if the armature flux were 
kept constant at 10,000,000 lines? Ans. 9,760,000 lines. 

E. M. F. = 104.2 volts. 

13. A shunt generator gives a full load current of 100 amperes at a 
terminal voltage of 125 volts, and an excitation of 20,000 ampere turns 
is required. To give the same voltage at zero load, 15,000 ampere turns 
are required. Find the number of turns required in a series field to 
give constant voltage. Ans. 50 turns. 

14. A series generator has a combined armature and field resistance 
of .1 ohm. It gives a terminal voltage of 98 volts with a current of 
20 amperes when driven at a speed of 1200 revs, per min. Find the 
terminal voltage when driven at a speed of 1500 revs, per minute it 
delivers a current of 30 amperes, if this current increases the field 
flux by 50#. Ans. 123 volts. 

15. A short shunt compound wound generator delivers 50 amperes of 
current at 110 volts at the terminals. Calculate the commercial effici- 
ency. Resistance of shunt field 55 ohms, of series field .02 ohm, of 
armature .14 ohm. All losses except copper losses equal 700 watts. 

Ans. 810. 



S 



CHAPTEE XIII. 
RUNNING GENERATORS IN PARALLEL. 

It is sometimes necessary to couple two or more generators to- 
gether so that they may supply to a circuit a larger quantity of 
electric energy than either could do singly. To increase the cur- 
rent it is usual to connect generators in parallel exactly in the 
same manner that electric cells are connected in parallel; that is, 
by connecting the positive terminals together to a common con- 
ductor and by connecting the negative terminals together or to a 
common conductor. 

Suppose a ship's plant was composed of three units of 800 
amperes each. As long as the current to be carried is below the 
capacity of one machine, it is very evident that only one machine 
would need be in operation. It would be better to allow the load 
on one machine to increase to its full capacity before starting 
another machine than to divide the full capacity of one machine 
between two machines, whether connected in parallel or not. A 
machine that is running at its rated capacity has a greater efficiency 
than when running at a reduced load. If one machine can deliver 
all the current necessary, besides the gain in efficiency, it is clear 
that there can be no good reason for running two, which would 
simply mean extra wear on the moving parts, extra lubrication, and 
the extra attention necessary from the dynamo tender. 

When the current necessary increases above the capacity of one 
machine, then it is obvious another machine must be connected in 
circuit. Suppose 1200 amperes were called for; this could be 
delivered by one machine at its full capacity of 800 amperes, and 
by a second machine running independently at 400 amperes. The 
case now becomes different, for two generators are necessary and 
whether running singly or in parallel, the wear and tear, oil con- 
sumption, and attention are practically the same. One would be 
running at its highest efficiency and the other at a considerably 



Euxxixg Generators in Parallel 211 

reduced efficiency. If any extra load was called for, it could only 
be thrown on the light loaded machine and this would involve extra 
care on the part of the tender that is not necessary, that of picking 
out the right bus bars to throw the switches on. This is a very 
slight matter, but it involves at least a question of time. If the 
two generators are connected in parallel, the total load of 1200 
amperes could be equally divided between them, so each would take 
600 amperes and the combined efficiency would be greater than 
when one is running at its highest and the other at a reduced 
efficiency. If extra load was now called for, it is immaterial on 
which bus bars the switches are closed, for all being in parallel any 
increase will be equally divided between the two machines. When 
the load is equally divided, there is a general balancing all around 
of the electric energy; no one part is being strained while another 
part is subjected to little or no strain ; the engines of the generating 
sets are doing an equal amount of work ; there is the same amount of 
loss in the field regulators, and the same heating effect in all the 
parts of the generator. Any sudden call for current falls on both 
machines alike and the evils, if there are any, of sparking and 
consequent shifting of the brushes are on each machine reduced 
by half. 

The two machines should be kept in parallel until their combined 
capacity is equal to the current called for, and if that still in- 
creases, a third machine should be connected in parallel with the 
other two. If 1800 amperes were required it could be furnished 
with two machines in parallel, each producing 800 amperes, and 
the third machine would then only have to supply 200 amperes, but 
if all three were connected, there would be 600 amperes on each, 
and there would be no danger of overloading any one machine, any 
current being added now being divided equally between the three. 

Connecting Shunt Machines in Parallel. 

There is no difficulty in running shunt generators in parallel, 
all that is necessary is to be sure to have the correct terminals con- 
nected together. The chief precaution to be observed is that when 
an additional generator is to be switched into circuit its field should 
be fully excited and the armature running at full speed before it 



212 Naval Electricians' Text Book 

is connected to the mains; otherwise the current from the mains 
might prevent the building up of the field and the induction of 
current. 

Suppose it is required to couple in parallel a shunt machine B 
carrying no load with another machine A carrying load, and that 
both are adjusted to the same terminal or switchboard voltage. 
The fields of both are fully energized and equal and the speeds 
relatively the same, so the total E. M. F. developed by the two 
armatures is the same. This total E. M. F. is equal to the terminal 
voltage plus the volts lost in overcoming the resistance of the arma- 
tures, in each case being equal to C a r a • When coupled in parallel 
so that A's load is one-half what it previously was, the armature 
current is halved and the lost volts in A are now only half as great 
as before. Consequently A's terminal voltage will rise, by the 
amount of half the original lost volts. 

The lost volts in B when running unloaded are equal to the field 
current times the armature resistance and are negligibly small. 
After coupling B now has half the original current and the lost volts 
increase to a value equal to the lost volts of A, and in consequence 
the terminal voltage of B will fall. 

Under these conditions, A would have a higher terminal voltage 
than B by an amount equal to the original lost volts of A, and A 
would still have the whole load and though B was in parallel, it 
would still be unloaded. If this difference existed in two machines 
that were each carrying approximately the same load before putting 
in parallel, the double load thrown on the one would produce 
serious results in heating and sparking if the circuit breakers did 
not properly function to open the circuit. 

The above discussion presupposes equal speeds, though if one 
was heavily loaded it would probably slow down and if the resulting 
difference of terminal voltages was not too great, the engine gover- 
nors might act to adjust the speed to bring the voltages within 
limits that the machine would take their equal share of load. 

Before throwing in a machine in parallel with another, in addi- 
tion to seeing that the polarity is the same in each, the terminal 
voltage of the one to be coupled should be 2 to 3 volts higher than 
the one carrying the load. 



Euxxixg Gexerators ix Parallel 213 

Connecting Series Machines in Parallel. 

Two series machines cannot be directly connected in parallel 
without some additional connections. If they were connected 
simply in parallel they might function if the E. M. F. at the 
terminals could be kept the same, and the internal resistances of 
each were exactly equal, but this could hardly occur. If the E. 
M. F. of one fell the slightest, current from the other would flow 
through the series coils in the opposite direction tending to weaken 
the current still more and reverse the polarity and in the end 
finally running it as a motor. To obviate this, not only the termi- 
nals of the machine are connected in parallel but the brushes are 
also connected by a conductor called the equalizer. If now either 
generator tends to slow in speed, current from the other will flow 
through the equalizer and through the series coils in the same 
direction as that of the generator itself, thereby building up the 
field and increasing the E. M. F. This equalizer also prevents any 
reversal of polarity, a very necessary precaution in parallel running. 

Connecting Compound Generators in Parallel. 

The only trouble in connecting compound generators in parallel 
arises from the series coils, the shunt being connected directly in 
parallel without any other connections, exactly as in the case of 
shunt generators. The series coils are connected with an equalizer 
exactly as in series generators, so for compound generators, it simply 
amounts to connecting the brushes of same polarity together as 
well as connecting the terminals. 

Necessity of an Equalizer. 

The equalizer helps to divide the load more exactly among the 
different machines. If there were no equalizer, as seen in series 
machines, the current from each armature would flow through its 
own series coil. When the load is increased, it might happen that 
one machine, being a little more sensitive than another, would take 
more than its share of the load, and this extra current going 
through its series coils would strengthen its field and cause it to 
generate more and more current, until it might blow its fuse and 



214 



Xaval Electricians' Text Book 



open the circuit. Another reason is given under the connection for 
series machines, that is, the difference of E. M. F. whereby one 
would tend to run another as a motor. 

Equalizing the Load. — By coupling all the machines to the equal- 
izer so that there is a common connection between the armature 
and the series coils, the currents from all the armatures unite and 
then divide among the different series coils. If one armature 
tends to deliver more than its proportion of the whole current, it 
strengthens the current in the series coils of all the machines and 




Fig. 85. — Parallel Connections. 

not its own alone. If one tends not to take its full share, some of 
the current from the other machines goes through its series coils 
and helps build up its field so that it delivers more current. 



Operating in Parallel. 

Fig. 85 shows the connections of a modern generator to the bus 
bars on the switchboard. R shows the rheostat in series with the 
shunt field, a field switch / being introduced in circuit. 

On the headboard there are two single-throw switches, one for 
each pole of the generator, represented by a, a. In addition, not 



Buxxing Generators in Parallel 215 

shown, there is a double pole circuit breaker and a switch for shunt- 
ing the series coils or for short-circuiting the series coils. On the 
switchboard, there are independent bus switches shown at ~b, b, for 
connecting the generator leads to the bus bars. The common equal- 
izer bus bar is shown under the current bus bars and to it is 
connected the equalizer from each generator through equalizer 
switches on the switchboard, shown at e, e. 

Suppose No. 1 is running singly and delivering current to the 
bus bars, then all the switches a, a, b, b, and f would be closed. 
It is desired to connect No. 2 in parallel with it. 

1. See all the switches on No. 2 open; these are, from the figure, 
the headboard, equalizer, bus bar switches, and field switch. 

2. Close equalizer switch e on No. 1. 

3. See that the resistance in field rheostat is turned to point 
marked " Low," all resistance out. 

4. Close the shunt field switch f. 

5. See that the voltmeter is connected on terminals for No. 2. 

6. Start engine and bring it up to speed (shunt field being ener- 
gized, E. M. F. will build up, and there being no resistance in 
rheostat will rise rapidly) . 

7. Move rheostat arm till E. M. F. rises considerably above the 
normal and then move it until it is about 2 volts above the normal. 

8. Close equalizer switch e on No. 2. 

9. Close bus bar switches on buses on which it is desired to 
run. 

10. Close right-hand switch a on headboard. (This must be the 
one that has the series field.) This excites the series field through 
the equalizer from the other machine. 

11. Close left-hand switch on headboard. (The one opposite 
to that which has the series field.) 

12. Eegulate load by field rheostat. 

To cut out a machine that is running in parallel with another, 
the opposite method of procedure is followed. 

1. Trip circuit breaker. (It is not necessary to open the head- 
board switches independently.) 

2. Open bus bar switches. 

3. Open equalizer switch. 



216 Naval Electricians' Text Book 

4. Turn rheostat and when voltmeter stops moving toward zero, 
open field switch. 

5. Stop the engine. 

Note. — For operating in parallel with standard switchboard, see under 
standard switchboard, Chapter XXIII.) 

In the switchboard that was the standard for many years (Fig. 
266) to connect in parallel, it was only necessary to see that the 
machines were poled alike, that they had the same E. M. F., that 
the load was approximately divided by means of the circuit switches, 
and the equalizing switch closed. Closing this switch, which 
is a double switch, connected one set of mains in parallel and con- 
nected the equalizers from each generator, the other set of mains 
being permanently connected. The load was afterwards adjusted 
by the shunt field rheostats. 






CHAPTER XIV. 
SERVICE GENERATORS. 

A generating set is a combination of an electric generator and its 
operating motive power. Generating sets used in ships of the 
navy consist of the generator and engine directly connected, so 
that both the engine and generator armature make the same number 
of revolutions. Up until very recently the motive power has been 
steam through the agency of the ordinary reciprocating steam 
engine, but at the present time, steam, through the agency of the 
turbine, is being utilized. 

Although the generator and its engine are considered as a unit 
in ship installation, their characteristics will be considered in 
different chapters. 

General Characteristics. — The general type of generator might 
be described as direct current, constant potential, multipolar, com- 
pound wound, this at once describing the type of armature winding 
(closed coil), as well as type and winding of the field. In the 
early days of electric installation on ships of the navy, a small 
bipolar machine was used, and this type may be found on a few 
vessels not built according to government specifications, and com- 
mercial generators of various designs may be met with in naval 
auxiliaries and colliers. All vessels built by or for the government 
are supplied with standard apparatus, built under specifications 
prepared by the Navy Department. 

The size of generators has steadily increased to meet the demands 
for increased power, and the increased current has necessitated new 
designs of armature winding, of armature conductors, new forms 
of frame and pole pieces, and a greater division of the magnetic 
field, and new designs for brush and holders to accommodate the 
increased number of brushes occasioned by the increase of current. 
From a small machine of 5 kilowatts power at 80 volts, generators 



218 Naval Electricians' Text Book 

have grown to a size capable of delivering 2400 amperes without 
overload, so that a machine that may be considered a standard for 
a number of years is soon superseded by one of another design. 

Forms of Field Magnets. 

There are several forms of these to be found, depending on the 
standard at time of installation, and figures of representative types 
are given. 

General Requirements. — Whatever the form, the material must 
be of the highest permeability, the greatest cross-section for a given 
weight, and of the softest iron consistent with mechanical strength 
and with the fewest number of joints. For small generators the 
frame is frequently of wrought iron, but in the larger sizes the 
lower part usually forms part of the generator frame or foundation, 
requiring it to be of cast iron or cast steel. 

Fig. 86 represents a type designed particularly for ships' use 
and called the Marine Generator, and it may be found on vessels 
built from twelve to fifteen years ago. This arrangement of pole 
pieces and field frame was particularly unusual, there being four 
internal and four external poles, and the winding of the field con- 
ductors was in one continuous coil on the side farthest from the 
commutator, and between the pole pieces. The idea of the internal 
poles was to allow induction in the inner portions of the armature 
conductors, as in the ordinary form of external poles only the outer 
portion is available for cutting lines of force. This peculiar 
arrangement only permitted the armature to be supported on one 
end of the shaft and though electrically it was correct in principle, 
in mechanical construction it was bad, and there were many in- 
stances of the sagging of the unsupported end of the armature, 
causing it to strike the pole pieces and break the insulation of the 
conductors. 

Fig. 87 represents a type also exhibiting peculiarities in con- 
struction, for in this the frame was built up of bars of iron instead 
of being solid, the idea being to get rid of the eddy currents induced 
in the frame and pole pieces. This was soon abandoned, for the 
difficulties and cost of construction outweighed any advantage 
gained by overcoming the eddy losses. 






Service Generators 



219 



Pig. 88 represents a type to be found in many vessels and exhibits 
good electrical properties, the frame and spool cores being all cast 
in one piece. The field spools are then slipped over the field cores 
and a curved pole piece bolted on. In this form there is very little 





Fro. 86. 



Fig. 87. 





Fig. 88. 



Fig. 89. 





Fig 



Fig. 91. 



stray field, the four magnetic circuits as shown by the dotted lines 
being compact and there are no joints to increase the magnetic 
resistance. It has the disadvantage of requiring the armature to 
be removed before any spool can be taken off for examination or 



220 Naval Electricians' Text Book 

repair, while the lower spool became the natural receptacle for dirt 
falling to the bottom. This spool frequently gave way in its insu- 
lation due to the dampness and oil that naturally found its way 
there. To get rid of these disadvantages the type represented by 
Pig. 89 was adopted. 

In this type all the field spools are more easily accessible, and 
the field frame being jointed in the middle, the upper part with its 
two spools can be lifted without disturbing the armature. This is 
a particularly good form and was a standard for a number of years. 

Fig. 90 represents a type that is used on a few of the smaller 
vessels, and is only different from Fig. 89 in the circular form of 
the frame and it possesses all the advantages of the other. 

Fig. 91 represents a type used on a few of the more modern 
generators and is different from the others in that the number of 
poles is increased. This is used on machines of large capacity or 
from which large currents are drawn, the total magnetic flux being 
divided into six separate magnetic circuits as shown by the dotted 
lines. The induction is divided among them and the loss is smaller 
than with a smaller number of magnetic circuits. The field is 
better balanced and the armature reactions are much lessened. It 
increases the number of brushes but this is a necessity on account 
of the large currents. 

Armatures. 

Under this head are included the armature core, the windings 
and the commutator ready for operation. For several years the 
standard armature for service generators was a modification of 
the Gramme-Paccinotti ring, a section of the ring in the direction 
of its length showing rectangular areas, and perpendicular to this 
direction a ring form. Fig. 92 is intended to show some of the 
details of construction, though not of any one particular type, as 
the different types had their own peculiarities of mechanical 
construction. 

Core. — The armature core is built up of thin laminations of soft 
iron, punched or cut to shape, each piece showing as a circular disc 
with a piece punched from 'the center. Their usual thickness is 
about one millimetre, the end ones being thicker to allow a good 



Service Generators 



221 



holding surface for the frame that holds them in place. The 
laminations are of the softest iron in order to reduce hysteresis loss 
as much as possible, and if they have been punched, they are after- 
wards annealed before final assembling. At the first assembling 
on the frame they are put in a lathe 
and turned smooth with a fine tool, and 
afterwards ground finer with fine files 
or by emery wheels. As in this style 
armature, conductors are wound di- 
rectly on the core, it is necessary that 
there should not be any small burrs or 
uneven surfaces left to cut the insula- 
tion of the conductors. Before final 
assembling the laminations are treated 
with a coat of enamel, and this need be 
but very light as the insulation is 
simply intended to reduce the eddy cur- 
rents, and the lightest insulation is 
sufficient to confine them to their own 
individual lamination. 

The laminations are finally assembled 
on a spider frame shown in the cross- 
section in the figure. The two ends of 
this frame are drawn together by bolts 
from one web of the spider frame to the 
other and when these bolts are set up, 
the laminations are drawn tightly to- 
gether. In some cases, the laminations 
are pressed together by hydraulic pres- 
sure and then held by the frame. The 
object in having the frame bolts 
through the frame and not through the 
laminations is to reduce any eddy cur- 
rents that might be induced in them, being placed inside the core 
where there is no magnetic field. The frame is of some non- 
magnetic material, bronze or gun metal, and is insulated from the 
end pieces, while the whole core is insulated with paper and mica 
before the conductors are wound on it. 




Fig. 92. — Ring Armature. 



222 Naval Electricians' Text Book 

Securing of Frame to Armature Shaft. — The spider frame is 
secured to the shaft by keys at each end imbedded in the shaft and 
frame, and it butts against a shoulder turned on the commutator 
end of the shaft and held against it by a locking nut on the other 
end of the frame. 

Cross-Connections of Armature. — In the four-pole machine, 
where there are two diameters of commutation, four sets of brushes 
would ordinarily be required, but by cross-connecting the arma- 
ture, only two sets are necessary. By this is meant the connecting 
of opposite segments of the commutator with conductors, these being 
soldered into opposite segments all the way around the commutator 
on the end nearest the armature. The function of these cross- 
connectors is to carry the current from the segment where a brush 
would have to be placed if not cross-connected to the segment on 
which the brush is resting. This connecting diametrically across 
the commutator brings the two sets of brushes used 90° apart. 

Conductors. — In the armatures that were standard for several 
years, the conductors are made up of stranded copper wires and the 
sizes calculated for an overload of 50 per cent. The stranded con- 
ductors are more flexible and the operation of winding the ring is 
made easier than if they were solid wires. The conductors are 
wound on the smooth core, forming a ring winding, after the core 
has been enameled and covered with heavy cotton and the latter 
shellaced or varnished and then thoroughly dried at a high tem- 
perature. In generators of this type in the smaller sizes, the con- 
ductors are laid in two or more layers on top of one another, but 
in the largest size, one layer was sufficient. The number of com- 
plete turns around the core for each segment of the commutator 
depended on the capacity of the generator and varied with their 
size, but were always laid to make a smooth surface on the outside 
of the armature. 

Connectors to Commutator. — There are no independent con- 
nectors from the armature conductors to the commutator, the 
conductors themselves being brought down and soldered solid into 
their proper segments, a hole being bored in the raised part of the 
segments for this purpose. They are pointed from the armature 
side of the commutator and the bared wires fitted into the holes 



Service Generators 223 

bored for them, and then soldered solid, so that the ends may be 
seen solidly connected. 

One or two forms of small generators have the connectors 
screwed on top to the commutator segments. 

Binding Wires. — After the armature is completely wound, the 
conductors are further secured on the core by binding wires, placed 
at equal intervals along the length and bound around the circum- 
ference. These wires are to prevent the conductors from being 
shaken loose and racked off when revolving at a high rate of speed. 
A strip of mica is laid on first around the circumference and the 
steel binding wire is wound over it, drawn taut and the ends 
soldered to the other turns of the winding. 

Insulation of Conductors. — The conductors are thoroughly insu- 
lated, dry cotton soaked in shellac being used and put on double, 
and in some cases the strands themselves are insulated in like man- 
ner one from another. 

Commutator. — There is not much difference in the commutators 
of the different types of the generators in use except as to size. 
They are made up of as many segments as there are separate coils 
on the armature, in some cases being as high as 350. 

The segments are made either of phosphor bronze or hard solid 
drawn copper of the highest conductivity. These are made to the 
proper shape and dimensions, each being of a cross-section of a 
sufficient size to carry the greatest current. The cross-section and 
the dimensions of the insulating material determine the diameter 
of the commutator. The segments are made slightly tapering in 
their width in order that the insulation may be of the same thick- 
ness throughout their depth. The insulation consists of several 
thicknesses of mica tightly pressed together, the segments and insu- 
lation being made of considerable greater diameter than the 
finished dimensions, both of them being turned down in a lathe 
and the whole surface smoothed with fine files and emery paper and 
then polished. 

The segments are held in place and prevented from flying off 
due to the centrifugal force of the rapidly revolving armature by 
collars which fit around the shaft and provided with projections or 
inclined shoulders that fit into similar shoulders made on the 



224 Naval Electricians' Text Booe: 

inside of each commutator segment. Bolts pass through these col- 
lars and on being set up, they tightly press the segments and hold 
them securely in place. This arrangement is shown in the figure. 

The segments are insulated with mica from the collars on the 
inside and also on the shoulders, the inside face usually being left 
clear of the outside of the collars, but, in some cases, also insulated. 

The collars are secured to the shaft by a feather and prevented 
from moving along the shaft by set screws through the collar into 
the shaft. 

Field Windings. 

The conductors composing the field are wound on spools made 
and shaped to fit snugly over the cores which are in one with 
the field frame. In some cases these spools are elliptical, others 
are oblong, and still others are circular. They are made of hard 
rubber or compressed paper or fibrous matter. Each spool is 
wound separately, both ends of each winding being left out where 
they are fitted with special leads and with clamp connections for 
joining to the windings of adjacent spools. These special connec- 
tions allow any spool to be disconnected from the others for pur- 
poses of examination, testing or repair. There are two separate 
windings on each spool, the series winding and the shunt winding, 
the windings being insulated from each other by cardboard and 
oiled cotton. The leads come out on opposite sides of the spool, 
the series leads being nearest the armature. It is immaterial which 
winding is put on first, but it is usual to wind the series first, being 
in the shape of heavy copper ribbon which readily takes the shape 
and lays flat and even on the inner surface of the spool. 

Insulation of Windings. — The series windings are usually insu- 
lated from each other by some form of unbleached cotton, and the 
shunt windings are usually single cotton-covered wire. 

Brushes. 

The number and size of brushes depend upon the current to 
be carried, and in machines of large capacity, to avoid having 
brushes of too great a size, the number is increased. The bipolar 
machines require but two sets of brushes, a set of brushes being 



Service Generators 225 

referred to as the number on each arm of the holder. In the 
four-pole machines which were the standard, and in which the 
armature was cross-connected, two sets of brushes are necessary, 
placed 90 degrees apart on the commutator. In some of these 
machines, there were two brushes per set, in others three, and in the 
largest there were four. 

Material. — The material is either copper or carbon, the former 
being used for several years, and was made up of copper gauze 
sheets pressed into shape. The completed brush of this material is 
more pliable than other forms, and there is not so much danger of 
the brushes cutting the commutator, due to too great tension, as 
the gauze easily bends. It also has the advantage of offering more 
collecting points for the current, as each little point does its share, 
this tending to reduce heavy sparking, as the whole current is 
divided into many little paths. The gauze form offers good oppor- 
tunities for ventilation, and it does not heat as readily as some 
other forms. 

Copper brushes are set at an angle to the normal to the com- 
mutator, the ends being beveled to lie flat on the commutator 
surface. 

Carbon brushes are used on a great many generators and in 
nearly all motors. They are made in the block form, except for 
small motors, and are set normally to the commutator surface. As 
the resistance of carbon is greater than copper, they heat more 
easily, but on this account they are made larger than would be neces- 
sary for copper brushes. They have no sharp points, so do not scar 
the commutator, and if properly adjusted will soon give the dark 
bronze polish to the commutator that is indicative of good condition. 

Brush Holders. — Brush holders may be said to consist of the 
rocker, rocker arm, and the brush holder proper, with the neces- 
sary springs and screw clamps for adjusting the brushes. These 
are of various designs and details, depending on the kind and num- 
ber of brushes used, but all must fulfill certain requirements. They 
allow the brushes to have a motion on the brush holder arm in a 
direction parallel to the commutator segments, being clamped by 
set-screws through the holder to the holder arm. Those using cop- 
per brushes have a small motion in the direction of rotation of the 



226 Naval Electricians' Text Book: 

armature, being clamped by screws in any desired position. This 
motion can be given to any brush independent of any motion given 
to the holder by means of the rocker arm. All holders are fitted 
with springs or screws by which the brushes can be held firmly but 
not rigidly against the commutator, and by w T hich the pressure 
against the commutator may be regulated. Most forms are fitted 
with " hold off " catches by which the brushes may be held clear 
of the commutator. 

After each brush is adjusted by its set and clamp screws and 
regulating spring, all the brushes together may be moved in a 
direction around the commutator by means of the rocker arm, 
through which motion is conveyed to the rocker and from that to 
the brush holders and to the brushes. The rocker arm can be 
secured in any position by means of a locking screw and the 
brushes held in any desired place. 

In the four-pole cross-connected armature the rocker consisted 
of a bronze frame in the shape of a quadrant of a circle, the holder 
arms being secured at right angles to it 90 degrees apart on the 
holder. The rocker arm was a straight spindle with a wooden or 
rubber handle, passing normally through the edge of the rocker, 
its central end being fitted with a thread which could be set up 
against the bearing on which the rocker turned. To move the 
brushes, it was only necessary to turn the rocker arm releasing the 
threaded end, and then moving the arm radially around the 
commutator. 

The holder arm is insulated from the rocker by hard rubber discs 
and cylinders, the generator leads being secured to the holder arms 
where they are secured to the rocker. 

Headboards. 

Standard machines of some years ago and of which many 
remain were fitted with w T ooden headboards, resting on the top 
piece of the octagonal framepiece. The current from the brushes 
is carried to terminals on this headboard by flexible bus con- 
ductors. From the headboard current is carried to the switch- 
board through a double-pole switch. There are separate terminals 
for the shunt and series windings, so either may be disconnected for 



Service Generators 227 

purposes of testing or repair, and, in addition, there is a separate 
terminal for the equalizing cable which connects through the 
switchboard to corresponding terminals of other generators. There 
is a separate terminal for the leading wire to the shunt field regu- 
lator, the other end securing to one of the shunt terminals. From 
the shunt field terminals were taken off connections for a pilot lamp 
over the headboard, which would glow while the main switch is still 
open, due to E. M. F. of the shunt current. This pilot lamp is 
useful as a means of telling when the field is commencing to build 
up and also insures light in the dynamo-room in case the main 
fuses blow or circuit breaker trips. 

Back of the headboard and secured in a wooden case is a variable 
resistance of heavy ribbon German silver connected as a shunt to 
the series winding. This is for the purpose of finally adjusting the 
E. M. F. in compounding the generator, and when once adjusted 
should not be further altered. It is usually in a locked case covered 
with a gauze top made for purposes of ventilation. 

Type M. P. 6-32-400-80. 

This type of generator is known as multipolar, 6 poles, 32 kilo- 
watts, 400 revolutions, 80 volts. It is a direct-current type and 
wound compound with long shunt connection. A detailed descrip- 
tion of this generator is given, partly because there are many of 
this type installed and partly because it is a good sample of a 
modern generator, but chiefly to illustrate the general character- 
istics of all generators, and to show the method of insulation and the 
care taken to prevent magnetic and electrical losses. If one is 
entirely familiar with such a generator, the understanding of others 
is made easier, and one should not be at a loss to know how to 
make repairs, to wind field coils or to renew armature windings, or 
to know what degree of insulation is necessary or the materials to 
be used. 

Field Frame. — Fig. 90 represents the form of field frames. The 
magnet frame is of cast steel and is made in two pieces, the lower 
of which is provided with bolts and set screws for use in securing 
proper alignment. The magnet cores are of soft steel of high 
permeability and are bolted to the magnet frame. A key which 





228 Naval Electricians' Text Book: 

forms part of the magnet core engages a key way in the frame and 
insures perfect alignment of the pole piece. 

The lower end of the magnet frame is provided with feet by 
which the frame is bolted securely to the generator foundation. 
The frame is insulated from the bed plate by a block of ash one 
inch thick with fiber bushings and removable washers around the 
securing bolts. 

Armature. — The armature of this generator is distinguished from 
others that preceded it by being drum 
wound, of the type known as a two-layer 
winding. The laminations forming the 
core have 77 slots punched at equal dis- 
tances around their peripheries, a view of 
one lamination showing a circular disc 
with 77 teeth. The laminations of the 
core are assembled on a spider frame of 
cast iron accurately fitted and keyed to 
the shaft. The spider frame is made 
p IG# 93, with flanges which project on each end 

beyond the laminations. The armature 
conductors are made of copper bars imbedded in the slots and run 
the entire length of the frame. Beyond the laminations and on 
the flanges the conductors are bent, and as there are six poles, each 
conductor is connected to one approximately 60 degrees around 
the circumference from it. The general form of a conductor is 
shown in Fig. 93. 

In this figure, the conductor is represented by a, h, c, &, the part 
h, c being imbedded in the slot, and the portions a, b and c, d on 
the flanges. These portions are bent to join the bent portions of 
other conductors around the armature to make the drum winding. 
On the end farthest from the commutator, the ends of the con- 
ductors are simply joined together; on the commutator end they 
are connected at their junction to the commutator segments. 

There are two layers of conductors in each slot, but as the layers 
from two slots are joined, although there are 154 conductors, there 
are only 77 connections on the front end, making 77 segments to 
the commutator. On the front end, an inner laver is connected to 



Service Generators 



229 



an outer layer 60 degrees from it, and on the rear end an outer 
layer is connected to an inner layer. The general plan of wiring 
is shown in Figs. 94 and 95. 

In Fig. 94 the full lines represent the bent portion of the con- 
ductors on the commutator end, the dotted lines on the rear end. 
The numbers on the outside of the circle are the number of the slots, 
those inside the number of the conductors, being 154 in all, two to 



TT ' 4 




each slot. This winding makes a closed coil, the winding con- 
tinuing through all the layers and ending at conductor 2, the start- 
ing point. Fig. 94 shows an inner layer joined to an outer layer, 
the outer layers of course being on top all the way around the 
circumference. 

Core. — The core consists of thoroughly annealed electrical sheet 
steel, 24 inches in diameter and .025 inch thick, the discs being 
magnetically insulated from one another. Inserted between the 



230 



Naval Electricians' Text Book 



laminations at intervals are space blocks, which are for the pur- 
pose of providing air ducts which communicate with the interior 
of the armature for cooling the core and windings. 

The bolts through the spider frame holding the laminations in 
place are secured so as not to pass through the laminations. 

Armature Insulation — Flange. — The flanges are insulated, first 
with a layer of muslin, then three layers of red paper and two layers 





Fig. 95. 



of oiled cotton, arranged alternately, and over all another layer of 
muslin. Over this last, layers of pressboard are placed and the 
flanges built up flush with the bottom of the slots in the lamina- 
tions. The insulation, with the exception of the pressboard, is 
carried over the edges of the flanges where it is pasted down. 

Slot. — In each slot in the lamination, the insulation consists of 
two layers of red paper and two of oiled cotton, arranged with the 
paper outside and the oiled cotton inside next to the conductors. 
This completed insulation, which is 0.35 inch thick, is held together 



Service Generators 231 

with shellac, and is of sufficient size to project above the conductors 
when they are in place and to fold over the top, and to project 
beyond the ends of the slot a sufficient distance to break joints with 
the flange insulation. 

This insulation is pressed into the slot before the shellac becomes 
dry. There are two parts of a coil in each slot and the insulation 
between them is red paper or leatheroid, cut slightly wider than the 
slot and pressed into place. 

The spaces between the upper and lower portions of the coils 
beyond the slots in the laminations on the flanges are filled with 
pressboard overlapped at the joints. 

After the coils are in place, the slot insulation is folded over 
the top of the conductors and in the notches in the upper part of 
the slots are driven hard wooden wedges, made of ash. 

Conductors. — The armature winding consists of 77 coils, each 
coil made of two bars .15" X .444" in multiple, with no insulation 
between the bars. The coils are insulated with cotton tape .009 
inch thick, put on ^ lap and then dipped in insulating japan and 
baked. There are two layers in each slot. 

Connectors to Commutator. — The commutator leads are of flex- 
ible copper, .04" X -75", bent so as to clamp the armature winding 
and firmly soldered into slots cut in the segments of the commutator. 

Binding Wires. — These are No. 13 B. & S. phosphor bronze wire. 
There are four bands, twelve turns per band, two over the front 
and two over the rear flange. Leatheroid is used between the 
binding bands and the winding. 

Commutator. — The commutator segments are supported on a shell 
which is directly attached to the spider. The bars are of hard 
drawn copper with insulation of selected mica not less than .03 inch 
thick. The bars are in line with the shaft and are secured by bolts 
and clamping rings. These bolts are accessible for tightening and 
removable for repair. The width of the commutator is 12 inches, 
the size of the segments on the circumference .7 inch, and depth 
of segments .75 inch. 

Field Windings. — The field spools for this machine are circular 
in shape and the series and shunt field coils are wound separately 
on the spools. The field spools are made of malleable-iron flanges 



232 Naval Electricians' Text Book 

riveted to a sheet-iron body. There' are three sets of series and 
shunt coils, three being wound in one direction and three in the 
other. The spools are held in position by projecting pole pieces 
upon the cores which are bolted to the magnet frame. 

Spool Insulation. — In this description, the cylindrical part of 
the spool is called the shell, and the two circular discs the flanges. 
The spool flange is first insulated by maple veneer board collars 
which are finished with one coat of japan, two of black shellac, and 
one of varnish. Before the collars are put in place, each end of the 
shell next the flange is insulated with four layers of muslin tape. 
The collars are then forced over this insulation to make a tight 
fit, any space between the edges of the collars and the insulation 
being filled with asbestos fiber which is afterwards saturated with 
boiled linseed oil. After the collars are in place, the shell is 
covered with four layers of oiled tape, two layers of oiled cotton 
and two la}<ers of red paper and a final layer of oiled tape. This 
insulation is cut the exact width of the space between the collars, 
and the last layer of tape is wound so as to well fill the corners 
and extend about \ inch up on the collars. After the winding is in 
place, the outside wires are japanned. The external diameter of 
the collars is greater than that of the flange, and where it projects 
over the flange it is rounded to give it a finish. 

Series Winding. — The series winding is wound on the insulated 
spool first and it consists of 4J turns of sheet copper, in three strips, 
wound in multiple. Two of these strips are .05" X 5" and one 
.04" X 5", and they are insulated from each other by unbleached 
percale of sufficient width to overlap the edges of the strips. 

The series leads for connection to the adjoining spools are made 
of copper strips .075" X 3", and are brought out next the flange 
nearer the armature and separated from the shunt winding by an 
insulating pad consisting of two thicknesses of varnished cambric 
and two thicknesses of red paper, extending \ inch on each side of 
the series lead and -} inch above the shunt winding. The leads are 
riveted and soldered to the series windings and should be brought 
out exactly diametrically opposite one another, and lead out along 
the insulating collars. 

The weight of each series coil is about 24 pounds, and with a 
cold resistance of .000105 ohm. 



Service Generators 233 

Shunt Winding. — The shunt winding is placed on the spool over 
the series winding, the two windings being separated by a pad com- 
posed of oiled asbestos, carboard, and oiled cotton. This winding 
consists for each spool of 725 turns of No. 9 B. & S. single cotton- 
covered wire, the whole weighing about 80 pounds, and has a 
resistance of about 1.58 ohms. 

The shunt leads are brought out on the flange away from the 
armature, and consist of two strips of copper, each .025" X .875". 
These terminals come out on the side of the spool towards the 
engine. The inner terminal is soldered to the wire by solder and 
rosin dissolved in alcohol. The outer terminal is secured under the 
last six turns of the winding. The last four turns are soldered to 
the terminal and the last two are soldered all the way around. 
The outer layer is coated with japan to preserve the coil from 
moisture. 

Series Shunt. — This is a resistance connected across the series 
leads of the generator, being made of several strips of German 
silver. When this is connected as a shunt to the series a portion of 
the main current flows through it. If its length is increased or 
cross-section diminished, its resistance is greater, and more of the 
total current will flow through the series windings, increasing the 
field. Increasing the cross-section or decreasing its length has the 
opposite effect, so by this the compounding of the generator can be 
regulated. When once adjusted for any particular range of voltage 
it should not be disturbed. 

Brushes and Holders. — In this generator, the commutator is not 
cross-connected, necessitating six sets of brushes, and in each set 
there are four brushes and four holders, these four being mounted 
on one holder arm. Fig. 96 shows the details of one brush and 
holder, all the others being identical with it. Carbon brushes are 
used, 11" X 1J" X W in size. 

The brush F is shown resting on the commutator and fitted in 
the box A, which is secured to the arm H, which in turn is secured 
to the arm G connected to the rocker. The brush is held down on 
the commutator by the flat copper spring I, on which is another 
flat copper spring B, resting on H and held by the screw-thread K. 
The top of the brush is connected to a pigtail connector E, a copper 



234 



Naval Electricians' Text Book 



conductor, which is clamped under a nut on the spring B at L. 
Tension on B and I is given by turning the milled head C, and by 
screwing that down the brush is held firmly against the commutator. 

The pigtail connector allows a free movement of the brush in 
the holder and avoids the resistance of imperfect contact that might 
exist between the brush and its box. 

To Renew Brushes. — To take out a brush, unscrew the stud D 
which frees the nut clamping the end of the pigtail connector E, 
and allows that end to be withdrawn through slots cut in B and I. 
Push the spring I forward, which will allow the connector to be 
easily withdrawn. Both springs B and / can then be pushed to one 




Fig. 96. 



side over the head of the brush, which can then be lifted out. In 
putting in or taking out a brush, it is not necessary to change the 
tension given by C, so the pressure on B and I need not be altered 
after once adjusted. 

Rocker. — The rocker for this generator consists of a circular 
frame with six radial arms from the central bearing which turns on 
the commutator bearing. This rocker looks somewhat like a steer- 
ing wheel, and to each end of the six radial arms is secured an 
arm at right angles to it holding the brushes, of which there are 
four to each arm. An extra spoke of this circular rocker is made 
with a handle, the central end fitted with a thread, which screws 
through the hub of the wheel to the bearing on which the rocker 
turns. This allows the frame to be turned and locked in any posi- 



Service Generators 235 

tion. The brushes are three positive and three negative, alternately 
arranged around the commutator, the three positive ones connected 
in parallel and the three negative ones in the same manner by 
connecting pieces in the form of arcs of circles. 

Form D Generator. 

This type of generator is the latest made under the standard of 
80 volts, all later ones being designed for 125 volts. It is known 
as M. P.-8-3 2-400-80 Form D, and is directly connected to the type 
of engine referred to under the chapter on Motive Power for Gen- 
erators, as 7^-12 X 8 Cross Compound, Form H Engine. 

Its principal difference from the type previously described is 
in the frame and poles, in the arrangement and connection of 
brushes, and in the headboard. The frame is circular in shape, 
divided longitudinally in its middle and so arranged that the upper 
half can be lifted clear of the armature. The lower half is fitted 
with two lug feet to secure it to the bed plate. 

There are eight projecting poles arranged equally around the 
frame_, fitted as previously described, and so spaced that one does 
not come in the vertical line through the center of the shaft, but at 
an angle of 22 \ ° from the vertical. Eight poles necessitate eight 
sets of brushes and four carbon brushes are fitted to each set. The 
brushes are held in holders from which project radial connecting 
leads to the connecting arcs. These arcs consist of two connecting 
bars of copper, of opposite polarity, almost the diameter of the field 
frame, fitted concentrically with the shaft, one behind the other. 
These arcs are of 270°, overlapping 45°. Every other set of 
brushes is connected to an inner and outer arc respectively, con- 
necting four alternate sets of brushes to one arc, the other four to 
the other arc. 

The connecting arcs are secured to and insulated from a circular 
rocker piece, one face securing the arcs, the other resting against 
and fitting in a groove in the edge of the field frame. This rocker 
piece is made light by cutting elongated holes in its side face. By 
revolving this rocker piece in the groove, both arcs and consequently 
all the brushes are moved circumferentially around the commutator. 



236 



Naval Electricians' Text Book 




Fig. 97. 

M. P.-8-32-400-80 Volt. Form D. Generating Set with 7%-12 x 8 Cross 

Compound, Form H, General Electric Engine. 



Service Generators 237 

Motion is given this rocker by a hand wheel fitted with gearing let 
in through the magnet frame, and also fitted with a locking wheel 
to lock the rocker in position. 

Headboard. — The generator leads are flexible conductors, one 
leading from each arc to the headboard. The headboard is fitted 
with single-pole circuit breakers, one in each lead, entirely inde- 
pendent of the other, with terminals for the shunt winding and its 
regulator, with a switch for short-circuiting the series winding if 
desired, with a pilot lamp, and with three terminals leading to the 
switchboard, one for each generator lead and one for the equalizer 
lead. On the back of the headboard is the usual series shunt. 

The headboard is secured to a frame mounted on the magnet 
frame directly over the armature. 

Most of the above details of this generator may be seen in the 
photograph shown in Fig. 97. This is shown connected to a Cross 
Compound, Form H, General Electric Co. Engine, described in 
the chapter on Motive Power for Generators. 

M. P.-6-16-450-125 Volt Type. 

This is one of the latest type of generators designed for ship in- 
stallation and is built under the following s|)ecifications of the 
Bureau of Equipment, Xavy Department: 

Specifications. 

Generator. 

1. To be of the direct-current, multipolar type, compound-wound 
long-shunt connection, designed to run at constant speed and to furnish 
a pressure of 125 volts at the terminals, at rated speed with load vary- 
ing between no load and one and one-third times rated load. 

2. The magnet yoke or frame to be circular in form, to have inwardly 
projecting pole pieces, and to be divided in half horizontally, in all 
generators above 5-kilowatts capacity, the two halves being secured 
with bolts, to allow the upper half with its pole pieces and coils to be 
lifted to provide for inspection or removal of armature. Pole pieces 
to be bolted to frame, bolts to be accessible in assembled machine to 
enable removal of field coils without disturbing armature or frame. 
Magnet frame to be provided with two feet of ample size to insure a 
firm footing on the foundation. 

3. Facilities for vertical adjustment of frame to be provided in sizes 
of 16 kilowatts and above 



238 Naval Electricians' Text Book 

4. Armature spider to be designed to avoid shrinkage strains. To be 
accurately fitted and keyed to shaft and to have ample bearing surface 
thereon. 

5. The discs or laminations to be accurately punched from the best 
quality thoroughly annealed electrical sheet steel, slot to be punched 
in periphery of laminations to receive armature windings. Discs to be 
magnetically insulated from one another and securely keyed to spider 
or held in some other suitable manner to obviate all liability of dis- 
placement due to magnetic drag, etc. Space blocks to be inserted be- 
tween laminations at certain intervals to provide ventilating ducts for 
cooling the core and windings. 

Laminations to be set up under pressure and held securely by end 
flanges. Bolts holding these end flanges must not pass through lamina- 
tions. 

6. The commutator bars or segments to be supported on a shell, 
which must be either part of or directly attached to the spider, to 
prevent any relative motion between the windings and these segments. 
Bars to be of hard drawn copper finished accurately to gauge. Insula- 
tion between bars to be of carefully selected mica and not less than 
0.03 inch thick, and of uniform thickness throughout. 

Bars to line with shaft and run true, to be securely clamped by means 
of bolts and clamping rings. Bolts to be accessible for tightening and 
removable for repair. 

7. Brushes to be of carbon. In sizes over 5 kilowatts there shall be 
not less than two brushes per stud, each brush to be separately remov- 
able and adjustable without interfering with any of the others. The 
point of contact on the commutator shall not shift by the wearing away 
of the brush. 

8. Brush holders to be staggered in order to even the wear over 
entire surface of commutator; the generator to be provided with some 
device for shifting all the holders simultaneously. All insulating 
washers and brushes to be damp proof and unaffected by temperature 
up to 100° C. 

9. Finished armature to be true and balanced both electrically and 
mechanically, that it may run smoothly and without vibration. The 
shaft to be provided with suitable means to prevent oil from bearings 
working along to armature. 

10. All copper wire to have a conductivity of not less than 98 per 
cent. 

11. The shunt and series field coils to be separately wound and sepa- 
rately mounted on the pole pieces. The shunt and series coils, respec- 
tively, of any one set to be identical in construction and dimensions 
and to be readily removable from the pole pieces. The shunt coils as 
well as the series coils are to be connected in series. 

12. In sizes of 16 kilowatts and above a headboard is to be mounted 



Service Generators 239 

on the generator containing the necessary terminals for main switch- 
board and equalizer connections, shunt and series field connections, 
pilot lamp. 

13. The field rheostat is to be of fireproof construction suitable for 
mounting on back of switchboard, with handle or wheel projecting 
through to front, either directly connected or by sprocket chain, handle 
to be marked indicating direction of rotation for raising and for lower- 
ing voltage of generator. The total range of adjustment to be from 10 
per cent above to 20 per cent below rated voltage, the variation to be 
not more than one-half volt per step at both full load and half load. 

14. A metal name plate to be fitted to the generator in a conspicuous 
place, to be marked as follows: 

Made for 
Bureau of Equipment 

by 

(Name of maker here.) 

Contract No. — . Req. No. — , 190 — . 

Type — . Class — . Form — . 

Generator No. — . 

Volts, — . Shunt Current, — . 

Amp., — . K. W. — . 

The number of the generator to be stamped on frame near name plate, 
for reference in case name plate is shifted. 

Operation of Generator. 

15. The compounding to be such that with engine working within 
specified limits, field rheostat and brushes in a fixed position, and start- 
ing with normal voltage at no load or at full load, if the current be 
varied step by step for no load to full load or from full load to no load, 
and back again, the variation from normal voltage shall at no point be 
in excess of 2 per cent of the normal voltage of the generator. 

16. The dielectric strength or resistance to rupture shall be deter- 
mined by a continued application of an alternating E. M. F. for one 
minute. 

The testing voltage for sets under 16 kilowatts shall be 1000 volts 
and for sets of 16 kilowatts and above shall be 1500 volts, and the 
source of the alternating E. M. F. shall be a transformer of at least 
5 kilowatts capacity for sets of 50 kilowatts and under, and of at least 
10 kilowatts capacity for sets of greater output than 50 kilowatts. 

The test for dielectric strength shall be made with the completely 
assembled apparatus and not with the individual parts, and the voltage 
shall be applied between the electric circuits and surrounding conduct- 
ing material. 

The tests shall be made with a sine wave of E. M. F., or where this 
is not available, at a voltage giving the same striking distance between 



240 



Naval Electricians' Text Book 



needle points in air, as a sine wave of the specified E. M. F. As needles, 
new sewing needles shall be used. During the test the apparatus being 
tested shall be shunted by a spark gap of needle points set for a voltage 
exceeding the required voltage by 10 per cent. 

17. With brushes in a fixed position, there shall be no sparking when 
load is gradually increased or decreased between no load and full load; 
no detrimental sparking when load is varied up to one and one-third 
times rated load; no flashing when one and one-third load is removed 
or applied in one stage. 

18. The jump in voltage must not exceed 15 per cent when full load 
is suddenly thrown on and off. 

19. The temperature rise of the set after running continuously under 
full rated load for four hours must not exceed the following: 





Method of 
measurement. 


Maximum allowable 
rise in °C. 






o 
331/3 
40 










333fe 

75 










40 









The rise of temperature to be referred to a standard room tempera- 
ture of 25° C. and normal conditions of ventilation. Room temperature 
to be measured by a thermometer placed 3 feet from commutator end 
of the generator with its bulb in line with the center of the shaft. 

20. The generator to be capable of satisfactory operation for a period 
of two hours carrying one and one-third times its rated full load, and 
no part shall heat to such a degree as to injure the insulation. 

21. Generators of the same size and manufacture to be capable of 
operation in parallel, the division of the load to be within 20 per cent 
throughout the range. The magnetic leakage at full load shall be 
imperceptible at a horizontal distance of 15 feet, measurements to be 
taken with a horizontal force instrument. 

22. The minimum allowable efficiencies of the generators are as fol- 
lows: 



K. W. 


Loads. 


1% 


1 


% 


^2 


2.5.... 

5 


Per cent. 

78 
80 
83 

87 
88 
88 
89 
90 


Per cent. 

78 
80 
83 
87 
88 
88 
89 
90 


Per cent. 
76 

78 
81 
86 
87 
87 
88 
89 


Per cent. 
73 
75 


8 


77 


16 


84 


24 


85 


32 


85 


50 


86 


1C0 


87 



A sectional view of a 50-kilowatt 125-volt generator built accord- 
ing to the above specifications is shown in Fig. 98. 



Service Generators 



241 




^ ^ 



Fig. 98. 
Marine Engine Cross Compound H-l, 50 Kilowatts, 7y 2 " x 14", 7" Stroke, 400 R. P. M. 



242 



Naval Electricians' Text Book 



Details of 100-Kilowatt Generator. 

A cross-section of the 100-kilowatt generator is shown in Fig. 99. 




Fig. 99. — Cross-Section of 100-Kilowatt Generator. 



Armature. 

The armature consists of the spider, core, commutator, and arma- 
ture windings. 

The spider is a casting of cast iron, ' composed of a hub and six 
legs radiating from the hub like the spokes of a wheel. The hub 
fits over the shaft whose diameter on the bearing surface is 5 inches, 
and is driven by the shaft by a keyway and driving feather, and it 
fits against a shoulder on the shaft nearest the driving flange, the 
diameter of the shaft being increased to 5^ inches. The legs of 
the spider are joined together by two cast-iron rings, one on each 
side of the legs, forming the rim of the wheel. These rings extend 
to the line of the slots in the core discs, and at the top they are 



Service Generators 243 

extended to form the flanges and to support the armature windings 
beyond the core, and on the bottom the}- are flanged around the 
T-shaped spider legs. The front and rear rings are secured by 
bolts passing through each and drawn together against space blocks 
on the core discs. 

Armature Core. — Between the two rings of the spider frame are 
secured the core discs; the core itself of a total length of 4| inches 
is made in two sections, which are separated from each other and 
from the rings by space blocks. These are metal castings consist- 
ing of a ring on which are radial arms carrying the blocks. The 
spaces left between the sections of the core discs and the spider 
heads afford a system of ventilation to the interior. 

The core discs are stamped from pure wrought iron and the core 
is built up from the discs, the laminations being .025 inch thick 
and are japanned for insulation before being assembled. The discs 
are held together by the pressure of the space block rings and are 
bored at the bottom for the bolts holding the spider head rings 
together. The core is positively driven by a ke\^ and feather on the 
outer face of the spider leg and inner diameter of the core. The 
slots for the armature windings are stamped in the discs before 
assembling and are afterwards trued up and made fair and smooth. 
Each disc is 2 J inches thick. 

The commutator is secured on an extension of the spider hub 
and fits against a shoulder made on the hub and is driven by a key. 
The shell comprising the body of the commutator is fitted with arms 
which allows air to circulate around them to the interior for pur- 
poses of ventilation. The outer surface of the shell is fitted with 
two rings, one on the front side, the other on the armature side, 
and bevelled as shown to receive the commutator bars. These rings 
are drawn together by through bolts, and thus the bars are held 
rigidly in place. The commutator bars or segments are lOf inches 
long, and there are 350 bars, two bars to a slot, and the finished 
diameter of the commutator is 30 inches. The bars are insulated 
from each other and from the shell by mica, and the ends of the 
bars nearest the commutator are milled to receive the connections 
from the armature windings. 



244 Naval Electricians' Text Book: 

Armature Windings. — The armature winding is of the multiple- 
drum type and consists of 1400 conductors of bar copper .07" X 
.075" arranged as shown in Fig. 101. Before being placed in the 
slots they are formed together in the Eickemeyer style of winding. 

Note. — This consists of a series of insulated coils formed exactly 
alike with the portions on the flanges of the armature so formed that 
there will be a space between the underlying portion of one coil and 
the overlying portion of the other where two adjacent coils cross. 

Field. 

The field consists of the frame, poles, and field windings. 

The details of the field are seen in Fig. 102, showing the dia- 
gram of connections. 

The frame is circular and is a casting made in two pieces. On 
the lower half of the casting are cast two feet which rest on a liner 
on the bed plate. The upper half is similar to the lower with the 
exception of the feet, and the two halves are secured together by 
invisible bolts on each side, the bolts entering through pockets in 
the brackets of the feet. 

The poles, ten in number, project inwardly from the field frame, 
and consist of the core over which secure the field windings, and 
the pole pieces or shoes. A cross-section on one pole is shown in 
Fig. 99. 

The core is a cylinder of soft cast steel, fitted against the interior 
curved surface of the frame to which it is secured by a single bolt 
which is tapped into the center of the core from the outside of the 
frame. This permits of the easy removal of any field magnet with- 
out removing the armature. The inner ends of the core form the 
pole pieces or shoes and are cast solid with the core, the ends fitted 
concentrically with the armature. 

The field windings are separately wound on spools which are 
slipped over the cores before these are secured in place and they 
are held by the projecting pole pieces. The shunt-winding spool 
goes on first, then the series. In each spool there is left an 
annular space for ventilation. 



Service Generators 245 

Brush Carrier and Connections. 

The brush carrier consists of a circular casting with lightening 
holes which fits into a recess on the commutator side of the frame 
and secured by screws. On the upper inner side is a toothed seg- 
ment which gears into a pinion on a shaft extending through the 
frame and which is operated by a hand wheel for varying the posi- 
tion of the brushes. There are two collector arcs for opposite 
polarity secured to the carrier, also the ten studs for the ten sets 
of brush holders. The brush leads for the total armature current 
are connected to the collector arcs and lead to hard rubber blocks 
secured to the top of the frame and shown in Fig. 102. One block 
carries the connection for the positive brush and switchboard leads 
and leads to the rheostat and the other carries the connection for 
the negative brush and switchboard leads and equalizer leads, and 
also lead for negative side of rheostat. 

Armature Insulation. 

Flanges. — Over the end of the flange is placed a layer of muslin, 
one end being allowed to remain hanging. Over this and extending 
the entire width of the flange are placed three layers of red paper, 
each .009 inch thick and two layers of oiled cotton, each .007 inch 
thick, arranged alternately, paper first. This insulation is of suffi- 
cient length to be folded over the end of the flange, where it should 
be pasted, after which the end of the muslin remaining hanging 
should be brought up and over this insulation, thus forming a 
finish. Over this, layers of pressed board should be placed and built 
up flush with the bottom of the slot. 

The arrangement of the insulation is shown in Fig. 100. 

Slots. — The insulation of each slot consists of one piece of .005- 
inch oiled .red paper cut to such a size that when pressed into the 
slot it will project about -J inch above the top of the slot and 
f inch beyond each end. After the coils are in place the insulation 
projecting beyond the top of the slot is trimmed off flush with the 
surface of the armature. 

Winding. — Each bar is taped with .005-inch tape butted through 
the slot part and one-half lap outside of the slot. Each bar is then 



246 



Naval Electricians' Text Book 



brushed with shellac over the slot part and the bars forming each 
group are molded together, after which they are covered along the 
slot part with 2J wraps of .006-inch varnished bond paper with the 
lap on the top. Over this is cemented a .010-inch piece of horn 
fiber with the edges butted in the center on the top of the coil. 
Between the upper and the lower layers of the winding in the slot 
is placed a .015-inch horn fiber separator which should project 
beyond the ends of the slot about f inch. Between the windings 
outside of the slots and over the flanges are placed .020-inch horn 
fiber separators, extending from the armature punchings to the 
inside of the clips which connect to the top and the bottom layers 




Paper 
Cotton 



Fig. 100. — Flange Insulation. 



of the winding. Over each of these separators is laid a narrow 
piece of .030-inch horn fiber placed close to the clips. No top sticks 
are used in the slots. 

The commutator leads are not taped, but are given a coat of 
air-drying japan. 

Binding Wire. — Over each section of the core are placed two 
bands of 10 turns each of .042-inch phosphor bronze wire, and 
over each flange two bands of 12 turns each of .072-inch steel wire. 

Field Winding. — The series winding consists of 6-J turns per 
coil of strip copper 2f" X .075", arranged 5 in multiple. The 
weight per coil is approximately 58 pounds; the cold resistance is 
.000118 ohm. 



Service Generators 



247 



The shunt winding consists of 585 turns of No. 10 B. W. Gr. 
single cotton-covered wire. The weight per coil is approximately 
72 pounds, the resistance cold .78 ohm. 

The two windings are placed side by side, the shunt winding 
being next the magnet frame. 

Insulation of Field Coils. 

Series Coils. — The coils are wound on forms. 
Before beginning the winding, .14" of pressed board is placed 
around the form to allow for wrapping space. 



.005 ffedfiaper, 
.O/o'tforn r/Aer 
.OOS'onen 7qpe 




0/5 Horn F/£>er <5eparator 
ween W/ntf/nga/ntSfot 



? 'Bet 



Fig. 101. — Insulation of Slot and Arrangement of Conductors. 



The "I" ("inside") series lead is first soldered on and insu- 
lated with a wrapping of five thicknesses (turns) of varnished 
cambric, each turn being coated with shellac to hold the turns 
together ; beneath the " I " lead are placed two thicknesses of var- 
nished cambric to prevent the rivet heads from working through 
the insulation on the bottom of the coil. The winding is then 
begun and a piece of .030-inch leatheroid is placed between the 
" I " lead connection and the first turn of copper. The first two 
turns of copper are insulated with one thickness of .008-inch muslin 



248 Naval Electricians' Text Book 

of sufficient width to lap over the top of each turn. This being 
done, the coil is clamped and removed from the form, and insulated 
by wrapping around it two layers of varnished cambric, half -lapped. 

A piece of 8-oz. duck is then sewed on under the " I " lead and is 
of sufficient length to extend to the top of the second turn of cop- 
per, under which the coil is wrapped with one thickness of 1-inch 
stay binding, half -lapped ; this done the coil is replaced on the form 
and wound with two turns of bare copper. Between these turns 
are placed the ventilating blocks of such thickness as will round out 
the coil ; the winding is then resumed, the .008-inch muslin insula- 
tion being placed between the turns. Then, before cutting the cop- 
per used in the winding, the " " (" outside ") lead is riveted and 
soldered on and is insulated in the same manner as the " I " lead. 
After this there are placed under the last turn six lots of four 
cords each of No. 7 boot thread, equally spaced, and extending 
about 12 inches beyond each side of the copper. 

Four of the copper strips are then cut off and the remaining 
strip is neatly covered with No. 2 cotton drill and wound com- 
pletely around the coil, riveted to the turn beneath it and cut off, 
after which the coil is removed from the form. Veneer collars are 
then fitted to the coil and holes drilled through them at the points 
at which the six lots of cord are located. The collars are then tied 
tightly to the coil by means of the cord before referred to, after 
which a lacing of cord, consisting of three turns, placed around 
each arm in the ventilating space, is tied and cut off. 

Shunt Coil. — On the form are placed two thicknesses of No. 2 
cotton drill of such a width as to cover the body of the form and 
extend up each side 3J inches. That portion of the drill extending 
up the sides of the form should be cut into small tongues of ap- 
proximately f inch in width ; the tongues in the two layers should 
be staggered. To the drill is added one thickness of .020-inch 
pressed board, three thicknesses of varnished cambric, and one 
thickness of oiled asbestos. Four layers of wire are then wound 
on the form and the tongues of the upper layer of the cotton drill 
are turned down over the winding. The winding is then continued 
until the ventilating space is reached, when the tongues of the first 
thickness of cotton drill are turned down and the winding is com- 



Service Generators 



249 



pleted to within two layers of the top of the coil. At this point 
pieces of cord are placed on the coil in the same manner as when 
winding the series coil, after which the winding is completed, the 
terminals are soldered on and the coil is removed from the form. 
The veneer collars are fitted and placed in the same manner as on 
the series coil. Both series and shunt coils are dipped in air-drying 
japan and thoroughly dried before being assembled. 



7b Positive 
crnd Pheostot\ 

Positive Line 



To Negative 

To Eq,ud/izer- 

7b Negative Lma 




Brushes under this Spoo/ 
to outside Bus Ping 



Commc/totor End 
Top View of Bottom Spoo/s 



Fig. 102. — Diagram of Connections. 



Compounding. 

The generator is compound wound and is provided with a shunt 
consisting of strips of German silver, to which are attached suitable 
terminals, which should be connected to the series terminals on the 
right-hand side of the machine facing the commutator. Any degree 
of compounding up to 10 per cent may be obtained by changing the 
length of the shunt. When the machine leaves the factory the 



250 



Naval Electricians' Text Book 



shunt is so arranged as to give the compounding called for by the 
specifications. 

Brushes. — Fit the brushes (Fig. 103) carefully to the commu- 
tator by passing beneath them No. sandpaper held closely against 
the surface of the commutator. Move the paper back and forth, 
being very careful to see that it does not leave the surface of the 
commutator while in motion, since in such a case, the edges of the 
brushes may become slightly rounded, and the results may be made 
unsatisfactory. A method of sandpapering the brushes, requiring 
a slightly greater length of time, but one which will insure good 




Fig. 103. — Brush Holder and Brush. 



results, is to move the sandpaper in the direction of the rotation of 
the armature, and on drawing it back for the next cut, raise the 
brush so as to free it from the paper; then lower it, and repeat the 
operation until a perfect fit is obtained. If the brush requires con- 
siderable sandpapering, No. 2 sandpaper may be used first, finish- 
ing with No. 0. 

Position of Brush-Holder Yoke. — The brushes should be set at 
no load, so that the reference mark on the pedestal is in line with 
the reference mark on the brush-holder yoke. With the brushes 
in this position, the generator will compound according to the name 
plate stamping. No movement of the brushes is necessary when 
load is thrown on or off. 



Service Generators 



251 



Method of Adjusting Type CS Brush Holders. 

Clamp the body of the holder firmly on the stud with the lower 
edge of the box -^ inch from the surface of the commutator. Care 
should be taken to see that the lower side of the box, A and A x 
(Fig. 104), is parallel to the surface of the commutator; in other 
words, the distance of the point A from the commutator should 
be the same as that of the point A t . The brush should then be 
inserted in the box and properly sandpapered and fitted to the 




Fig. 104. — Brush Adjusting, 



surface of the commutator. The pressure on the brush should be 
from 1J to 2 pounds, and can be easily adjusted by placing the 
adjusting lever in one of the various notches. 

Equalizing Rings. 

A feature of the 100-kilowatt generator is the use of equalizing 
rings on the back of the armature. The object is to maintain the 
brushes of the same polarity at the same potential. Brushes of the 
same polarity may have differences of potential due to difference 
in the pole strengths at the two poles, to differences in winding, or 
the brushes may make unequal contact on the commutator. If two 
brushes are at different potentials, current will flow from one to the 



252 



Naval Electricians' Text Book 



other through the brushes, and the result of unbalanced current is 
bad sparking and excessive heating. The equalizing rings are con- 
tinuous conductors secured in the back of the armature and insu- 
lated from it. Leads from the winding at the periphery connect 
from parts of the winding which in the different sections will be 
in the same position in regard to the fields. Hence, if any differ- 
ence of potential exists current will equalize through these rings 
rather than through the brushes. 

A diagrammatic sketch of these rings is shown in Fig. 105, from 
which the action can be understood. 




Fig. 105. — Connection of Equalizer Rings. 



Specifications for 300-Kilowatt Generator Used with Turbine. 

Generator. 

1. To be of the direct-current, multipolar type, compound-wound long- 
shunt connection, designed to run at constant speed and to furnish a 
pressure of 125 volts at the terminals, at rated speed with load varying 
between no load and one-third times rated load. 

2. The magnet frame will be circular in form; will have inwardly 
projecting pole pieces and will be divided in half horizontally, the two 
halves being secured with bolts to allow the upper half with its pole 
pieces and coils to be lifted to provide for inspection or removal of 
armature. The pole pieces will be bolted to the frame. 

The magnet frame will be provided with two feet of ample size to 
insure a firm footing on the foundation. 

3. Facilities for vertical adjustment of the frame will be provided. 

4. The laminations for the armature will be accurately punched from 



Service Generators 253 

the best quality thoroughly annealed electrical sheet steel, slots to be 
punched in the periphery of laminations to receive armature windings. 
The laminations will be insulated from each other and will be assem- 
bled on the spider or shaft and securely keyed. Space blocks will be 
inserted between laminations at certain intervals to provide ventilat- 
ing ducts for cooling the core and windings. Laminations will be set 
up under pressure and held securely by end flanges. 

5. The commutator bars will be supported on the shell which will 
be keyed directly on the shaft so that no relative motion can take place 
between the windings and bars. The bars will be of hard drawn cop- 
per finished accurately to gauge. The insulation between bars will be 
of carefully selected mica or commutite of not less than .03 inch thick. 
The bars will line with the shaft and run true and will be securely 
held in place by means of clamping rings. 

6. The brushes will be of carbon. Each brush will be separately 
removable and adjustable without interfering with any of the others. 
The point of contact on the commutator will not shift by the wearing 
away of the brush. 

7. Brush holders to be staggered in order to even the wear over 
entire surface of commutator; the generator to be provided with some 
device for shifting all the holders simultaneously. All insulating 
washers and brushes to be damp proof and unaffected by temperature 
up to 100° C. 

8. Finished armature to be true and balanced both electrically and 
mechanically, that it may run smoothly and without vibration. The 
shaft to be provided with suitable means to prevent oil from bearings 
working along to armature. 

9. All copper wire to have a conductivity of not less than 98 per cent. 

10. The main and commutating coils, respectively, of any one set 
to be identical in construction and dimensions and to be readily remov- 
able from the pole pieces. The shunt coils as well as the series coils 
are to be connected in series. 

11. A headboard will be mounted on the generator containing the 
necessary terminals for main switchboard, equalizing connections, 
shunt and series field connections, and pilot lamp. 

12. The field rheostat to be of fireproof construction suitable for 
mounting on back of switchboard, to be provided with handle or wheel 
projecting through to front, either directly connected or by sprocket 
chain, handle to be marked indicating direction of rotation for raising 
and for lowering voltage of generator. The total range of adjustment 
to be from 10 per cent above to 20 per cent below rated voltage, the 
variation to be not more than one-half volt per step at both iull load 
and half load. 



254 Naval Electricians' Text Book 

13. A metal name plate to be fitted to the generator in a conspicuous 
place, to be marked as follows: 

Made for 
Bureau of Equipment 

by 

{Name of maker here.) 

Contract No. — . Req. No. — , 190 — . 

Type — . Class — . Form — . 

Generator No. — . 
Volts, — . Shunt Current, — . 
Amp., — . K. W. — . 
The number of the generator to be stamped on frame near name plate 
for reference in case name plate is shifted. 

Operation of Generator. 

14. The compounding to be such that with turbine working within 
specified limits, field rheostats and brushes in a fixed position, and 
starting with normal voltage at no load or at full load, if the current 
be varied step by step from no load to full load or from full load to no 
load, and back again, the difference between maximum observed voltage 
and minimum observed voltage shall not exceed 2^ volts. 

15. The compounding and heat run (full load and overload) of the 
generating sets must be made with identical brush positions. 

16. The dielectric strength for resistance to rupture shall be de- 
termined by a continued application of alternating E. M. F. of 1500 
volts for one minute. Test for dielectric strength shall be made with 
the completely assembled apparatus and not with the individual parts 
and the voltage shall be applied between the electric circuits and sur- 
rounding conducting material. 

17. With brushes in a fixed position there shall be no sparking when 
load is gradually increased or decreased between no load and full 
load; no detrimental sparking when load is varied up to one and one 
third times rated load, no flashing when one and one-third load is 
removed or applied in one stage. 

18. The jump in voltage must not exceed 15 per cent when full load 
is suddenly thrown on and off. 

19. The temperature rise of this set, after running continuously 
under full rated load with air of auxiliary ventilation at room tem- 
perature for four hours must not exceed the following: 

Degrees 0. 
Armature, by thermometer 40 

Commutator, by thermometer 45 

Series field coils, thermometers 40 

Shunt field coils by resistance 40 

Shunt rheostat, resistance method 75 

Series shunt, thermometer 40 



Service Generators 255 

The rise in temperature to be referred to a standard room tempera- 
ture of 25° C. Room temperature to be measured by a thermometer 
placed three feet from commutator end of the generator with its bulb 
in line with the center of shaft. 

20. A system of air ducts for the ventilation of armature and com- 
mutator shall be provided. This system shall be connected to the ship's 
ventilating system. The amount of air per minute required for the 
various sized sets will not exceed the following: 

Size of K . W. Cubic feet air per minute. 

300 3000 

21. The generator to be capable of satisfactory operation for a period 
of two hours carrying one and one-third times its rated full load; also 
full load continuously in a room temperature of 35° C, without aux- 
iliary ventilating system, and no part shall heat to such a degree as to 
injure the insulation. 

22. Generators of the same size and manufacture to be capable of 
operation in parallel, the division of the load to be within 20 per cent 
throughout the range. The magnetic leakage at full load shall be im- 
perceptible at a horizontal distance of 15 feet, measurements to be 
taken with a horizontal force instrument. 



CHAPTEE XV. 



THEORY OF MOTORS AND MOTOR CONTROL. 

An electric motor may be defined as an electric machine by which 
electric energy in the form of electric currents is converted into 
mechanical energy by the operation of conductors carrying currents 
revolving in a magnetic field. Machines are divided into types of 
constant potential, constant current and alternating current as in 
the case of generators, but as the system of supply on board ship 
is of constant potential and continuous current, only such types that 
come under that head will be considered and their general prin- 
ciples explained, together with some of the uses to which they are 
applicable. 

General Principles. 

The elementary principle of the generator was explained by the 

action of a straight conductor 
moving across a magnetic field, 
and in which it was shown that 
the power used to move the con- 
ductor was converted into elec- 
trical energy, while at the same 
time it overcame a force which 
exerted a drag on the conductor. 
If the conductor is supplied 
with a current from an external 
source the same drag exists on 
the conductor and if not over- 
come will cause the conductor 
carrying the current to move across the magnetic field. This 
motion will itself generate an E. M. F. in the conductor, which by 
Lenz's law tends to stop the motion of the conductor. 

In Fig. 106, current is forced by some external means through 




Fig. 106.- 



-Illustrating the Principle 
of the Motor. 



Theory of Motors axd Motor Coxtrol 257 

the straight wire AD fitted to slide along the portions AB and CD 
and to form portion of a closed circuit ABCD. The whole circuit 
is placed in a uniform magnetic field of intensity E, perpendicular 
to the plane of the paper. 

A C. G. S. unit of current exists when one centimetre of its con- 
ducting length is urged across a magnetic field of unit intensity 
with a force of one dyne. 

If the length of the conductor AD is 1 centimetres, and strength 
of current C absolute amperes, then the force urging the con- 
ductor across the magnetic field is 

F = E1C dynes. 

The work done by this current moving the conductor at the rate 
of v centimetres per second is Fv ergs. 

The motion of the conductor through the magnetic field induces 
in the conductor an E. M. F. (since E. M. E. is equal to the num- 
ber of lines of force cut per second) equal to 

E = Elv absolute volts, 

and this E. M. E. opposes the flow of current in the conductor. 

The work done by the current is Fv ergs, or 

Fv = HlCveTgs; 

and since E = Elv, the work done = EC ergs per second, or 

work done = EC watts. 

The work spent by the current goes to keep up the motion of the 
conductor. 

Application to Practical Apparatus. — The general principle upon 
which all electric motors work is that a conductor carrying a cur- 
rent will, when placed in a magnetic field, tend to move in such a 
direction as to embrace the greatest possible number of lines of 
force. 

Having seen the general principles under which generators work, 
we shall best understand the motor by considering it as a generator 
worked backwards ; that is, a magnetic field is produced by an 
electric current, and currents are made to circulate in conductors 
wound on an armature, being supplied from some outside source. 



258 



Naval Electricians' Text Book 



The conductors carrying currents produce magnetic fields around 
them, and the resultant of these two fields tends to move the con- 
ductor, and if properly arranged mechanically, to produce rotation. 
Figure 107 represents two conductors lying in the air spaces be- 
tween two magnet pole pieces N and 8 and a cylindrical magnetic 
core. The air space is a magnetic field due to the poles N and S, 
the field due to these poles being represented by the straight lines 
running from right to left through them and the iron core, the 
positive direction being indicated by the arrow heads. The two 
conductors are marked, one UP representing a current flowing 
towards the observer as the figure is viewed, the other DOWN, 
flowing away from the observer. 





Fig. 107. — Separate Magnetic Fields. 



The positive direction of the magnetic field due to the current 
marked UP is, according to the laws of induction, anti-clockwise 
viewed from this side and is shown as a series of concentric circles 
around the conductor. The field due to the current marked DOWN 
is similarly shown, the positive direction being clockwise. These 
two independent conductors may be considered to form part of a 
closed coil, the current running down on one side, through a con- 
necting piece on the end of the core, parallel to the lines of force 
due to N8 and up on the other, the two ends being connected with 
the source of supply of current. 

If the magnetism of N and S is steady and the current through 
the coil is continuous and steady, the figure would represent the 



Theory of Motors axd Motor Coxtrol 



259 



effect, as far as the lines of force are considered, if there were no 
reaction between the fields. But there is reaction between them, 
the result being a compound magnetic field representing the result- 
ant of the forces due to the poles and the forces due to the currents 
flowing in the conductors. 

Fig. 108 shows the resultant field in the air spaces due to the 
magnetic field of the poles and the fields due to the current flowing 
in the conductor under the same conditions as stated above. The 
resultant field may be shown experimentally or the resultant direc- 
tions of the lines of force may be proved mathematically. Eemem- 
bering that the lines of force tend to shorten themselves, there 
being tension along them and pressure at right angles, it is clear 





Fig. 108.— Resultant Magnetic Field. 



that the pressure of the lines above the conductor marked UP will 
tend to force that conductor towards the bottom of the page as 
shown by the arrow, and similarly the conductor marked DOWN 
will be urged towards the top of the page. 

If these conductors form part of a coil and are secured to the 
core which may be balanced on a shaft, the pull on one side and the 
push on the other side of each conductor will tend to cause revolu- 
tion of the core. The tendency to revolve will be measured by the 
product of the force due to the current and the horizontal distance 
of the conductor from the center of the core. As the coil revolves, 
the horizontal distance between the conductor and center becomes 
smaller, approaching zero, which it is when the two conductors are 



260 Naval Electricians' Text Book 

vertically over one another. The arm now being zero, the tendency 
to turn is zero, or the conductors will come to rest. In this posi- 
tion, the coil is now embracing the greatest number of lines due to 
the magnets, illustrating the principle already stated that a con- 
ductor carrying a current placed in a magnetic field will tend to 
move so as to embrace the greatest possible number of lines of force. 

By arranging a series of coils around the core it is very evident 
that continuous rotation would be the result, for when one coil was 
in the position of zero tendency to turn, one at right angles would 
be in position of greatest tendency. 

Torque.— It has been shown that the force developed by the cur- 
Tent flowing in the conductor is dependent upon the intensity of the 
field, the current flowing, and the length of the conductor, or 

F = BIO dynes. 

This force acts at right angles to the conductor and directly on 
it, and the total force developed is called the drag on the conductors. 
It is the force of this drag applied at the radius of the circle repre- 
senting the cross-section of the core on which the conductors are 
wound that gives rise to the tendency to turn about a fixed axis. 
This tendency to turn is the twisting moment and is called the 
torque. 

The torque is the product of two factors, force and distance, 
which produce work. 

Distance or length divided by time gives velocity and work 
divided by time gives power. 

work = force X distance 

work „ v , distance 

= force X —p ? 

time time 

or power = force X velocity 

= force X radius X -, • ' 
= torque X angular velocity. 
The power absorbed by a motor is, as in the case of the power 

developed in a generator, the product of volts and amperes ; 

or volts X amperes = torque X angular velocity. (1) 



Theory of Motors and Motor Coxtrol 261 

The angular velocity is expressed in radians per second, a radian 
being the angle whose arc equals the radius, so in one revolution 
there are 2?r radians, and the expression for angular velocity is 2-n-n. 

Substituting in equation (1), we have 

27rnT 
watts = 107 

where T is the torque expressed in ergs, and 1 watt = 10 7 ergs per 
second. 

If T is expressed in ft.-lbs., we have 

watts = 2irnT X 1.356. 
Since 1 H. P. = 746 watts 

= 550 ft.-lbs. per second, 
or 1 ft.-lb. = 1.356 watts. 

Since E = 108 volts 

1 — 1.356 X 10 8 X &r" W 

Expression (2) shows the important fact that the torque is inde- 
pendent of the speed, and depends only on the current flowing 
through the armature and on the magnetism. 

Eef erring again to equation (1), as the torque depends on the 
current, the speed must depend on the volts, giving the two im- 
portant facts ; first, that the torque developed by a motor depends 
on the current absorbed and, second, that its speed depends upon 
the E. M. F. at the terminals of the motor. 

Applied and Counter E. M. F's. 

In Fig. 109 suppose there are two machines in all respects alike 
as to the winding of their armatures, and the fields of each are 
permanent, either due to permanent magnets or from current from 
some external source. The armature of the motor M, is directly 
connected to that of the generator J), and is supplied with current 
from it. If the armature of M is stationary, the only E. M. F. 
required to send a current through the conductors is that due to the 
resistance of the armature winding. If the torque due to this cur- 
rent is greater than the resistance to motion around the axis, the 
armature of M will turn, as explained. 



262 



Naval Electricians' Text Book 



The motion of the armature coils of M through the magnetic 
field induces an E. M. F. exactly similar to the case of the gen- 
erator, and a consideration of the relative directions of the lines 
of force and of rotation will show that this E. M. F. is opposed to 
that of D. In each case, the windings of D and M are such that 
the induced current for the same direction of rotation tends to flow 
towards the upper brush, so the E. M. F. generated by M is opposite 
to that developed by D. 




Pig. 109. — Illustrating Counter B. M. F. 



The E. M. F. of the supplying generator is called the applied 
E. M. F. and the opposing E. M. F. the counter E. M. F. or 
C. E. M. F. 

The counter E. M. F. cannot be measured directly, as a volt- 
meter connected to the motor terminals would show the same 
voltage as that of the generator terminals, less the drop in the 
leading wires. 

In a generator, the torque is supplied by the mechanical power, 
being opposed to and overcoming a counter torque that is acting 
on the armature conductors; the overcoming of this counter torque 
being a measure of the power necessary to drive the armature. 



Theory of Motors and Motor Control 263 

Here in the motor we have the opposite effect, the E. M. F. sup- 
plied by the external source being opposed to and overcoming a 
counter E. M. F., and this counter E. M. F. being a measure of 
the power absorbed by the motor. 

The counter E. M. F. being opposed to the applied E. M. F. 
diminishes its effect, so that the current through the armature is 
lessened and consequently the torque is less as the speed is in- 
creased. If the torque is still greater than the opposition to 
motion, the speed of the armature will increase, the current and 
torque decrease, until the torque exerted by the current is just 
equaled by the resistance to motion, of whatever nature that may be, 
when the speed will remain constant. So we see at the outset the 
important principle that the greater the speed the less the torque to 
produce the same amount of power. 

When the speed becomes constant, the difference between the 
applied and the counter E. M. F. represents the drop through the 
armature, or the difference of potential required to force the cur- 
rent through the armature resistance. The product of this differ- 
ence of potential and armature current represents the energy lost 
in heating the armature coils. This becomes greater as this differ- 
ence increases and is a maximum when the armature is at rest, 
when there is no counter E. M. F., so it is seen that at this time, if 
the armature does not turn, all energy is lost, and a very large 
current would flow, so large in fact as to endanger the armature. 
On this account it is usual to insert in series with the armature 
current a resistance called a starting resistance which is made large 
enough to allow a small current to flow at first, producing an initial 
torque, and as the speed increases and counter E. M. F. increases 
so as to reduce the current, the starting resistance is gradually 
lessened, until at full speed when very little current is flowing 
through the armature, all the resistance is out. 

Of the total E. M. F. applied to the motor, part is expended in 
overcoming the resistance of the armature, and is energy lost, while 
the difference, or the counter E. M. F. represents the energy re- 
quired to keep the armature in motion, and represents the energy 
expended in overcoming friction losses and core losses, exactly as 
in the case of the generator, and in overcoming the resistance to 



264 Naval Electricians' Text Book 

motion of whatever nature that may be; this latter being the 
mechanical work done by the motor. 

To a certain extent the motor is entirely automatic as regards 
relation of current to external load. A certain amount of current 
is' necessary at all speeds to furnish the torque necessary to over- 
come the motor losses, and if there is not sufficient current to over- 
come these losses, there will be no motion. Suppose the motor is 
running at a certain speed with a certain load, or doing a certain 
amount of external work, then if the load is increased, the current 
flowing at that time cannot furnish sufficient torque to perform this 
extra work, so the motor slows down. This slowing down reduces 
the counter E. M. F. and consequently the current increases, and 
the torque is now sufficient to perform the extra work the motor 
is called on to do. If the load is decreased, the armature has too 
much torque, so it speeds up, thereby increasing the counter E. 
M. F. and decreasing the current, and thereby the torque to the 
proper amount. 

All that has been said regarding motors so far has reference to a 
field of practically constant value, in the theoretical case, the field 
being supplied by some constant potential source. In practical 
applications the field magnets of constant potential motors may 
be either shunt wound or series wound, or a combination of these 
two, corresponding to the compound-wound generator, called differ- 
ential wound. 

Fundamental Equation of the Motor* 

The E. M. F. induced by a motor armature revolving in a mag- 
netic field is calculated in exactly the same manner as that for a 
generator, and in general terms is 

E = nZN, (3) 

where the symbols have the same signification as previously given. 
Equation (3) represents the motor E. M. F. or counter E. M. F. 
The difference between the applied E. M. F. and the counter E. M. 
F. represents the drop in voltage that takes place in the armature 
resistance and is equal to C a r a , and, therefore, 

g — E = C a r fl , 
or 6 = nZN + C a r a . (4) 



Theory of Motors axd Motor Coxtrol 



26: 



Eef erring to the fundamental equation to the generator, the Z 
used in equation (4) is 1—j- where p and p' have the same significa- 
tion as there given. 

From equation (4) 



P 



and 



C a = 



g — C a r a 
ZN 

(S — nZN 
r* 



(5) 



(6) 



Equation (6) shows that C cannot be calculated from Ohm's 
law in a running motor, and only holds when n = 0, 



when 



r _ @ 

U a — 



Under this condition, owing to the small value of r a , C a would be 
excessive, necessitating the insertion of the starting resistance in 
series with the armature. 



Fig. 110. — Elementary Shunt Connections. 



Shunt Motors. 

The elementary connections of a shunt-wound motor are shown in 
Fig. 110, though it must be understood that this is given for a 
machine that is running; the starting requiring a separate device. 

In the figure, L x and L 2 represent the supply mains, M the motor 
armature, and S the shunt field. 

In shunt-wound motors from a constant potential source of 
supply, the difference of potential at the field terminals being con- 
stant, the magnetizing force is constant and all that has been said 



26t3 Naval Electricians' Text Book 

in reference to motors in general will apply to this case. The field 
being constant, the counter E. M. F. will depend on the speed, and, 
as has been shown, the amount of current taken varies automatically 
with the external load, and variations in load will make but slight 
changes in speed. There is no danger of a shunt-wound motor 
attaining such a speed as to become dangerous, for as it tends to 
speed up, the current and consequently the torque is decreased, and 
it will only attain a speed- such that the torque just balances the 
friction or whatever the resistances to motion may be. 

On account of the small variations in speed, shunt motors are 
used where nearly a constant speed is necessary or on moving parts 
that would be damaged if the speed became excessive, such as on 
portable fans, or ventilating sets, or pumps, and on machinery 
where there is not much starting and stopping, or where excessive 
torque is not required at starting. One disadvantage of the shunt 
motor is that, the field being always constant, there is always a 
constant loss of energy. 

The previous explanation may be seen from an examination of 
the formulae deduced. 

When a shunt motor is running light or unloaded, the torque 
required to drive it is only that necessary to overcome the friction 
of the bearings and air friction, and is consequently small, and from 
equation (2) C a must be very small. Consequently the drop 
through the armature C a r a must be very small and can be neglected, 
since both C a and r a are very small, and from equation ( 5 ) 

n = ^r at zero load. (7) 

As nZN is equal to E, the applied E. M. F., it is seen that at 
zero load, a shunt motor runs at such a speed as to make its counter 
E. M. F. sensibly equal to the applied E. M. F. 

When load is thrown on a shunt motor, the tendency is to slow 
somewhat and thereby decrease nZN, the counter E. M. F. Ac- 
cording to equation (6) C a will then increase, as will also the 
torque T according to equation (2), and it is the increase of the 
torque which enables the motor to carry the increased load. The 
decrease of counter E. M. F. must be sufficient to allow enough cur- 
rent to flow to develop the necessary torque. If N is constant, 



Theory of Motors and Motor Control 267 

nZN could only vary by a drop in n, but due to demagnetizing 
action of the armature current, N varies, so the change in nZN is 
produced both by N and n, so the actual change in the speed is 
less than if the field was absolutely constant. 

Relation Between Field and Speed. — If the field is decreased, 
nZN, the counter E. M. F. is decreased, and a sudden increase of 
armature current results, as shown by equation ( 6 ) . The increased 
current produces more torque than is necessary to carry the load, so 
the motor speeds up until the increase of nZN reduces the current 
to the value to give the required torque. 

Relation Between Brush Lead and Speed. — A generator has its 
maximum E. M. P. when the brushes are at zero lead, or have no 
lead. In the case of a shunt motor, the speed is a minimum when 
the brushes have zero lead, and any movement of the brushes either 
forwards or backwards, will increase the speed and this is particu- 
larly noticeable in a motor running light. 

When the brushes are moved from the zero position, the counter 
E. M. F. is reduced, the speed remaining unchanged. As a result 
a greater current flows, producing an increased torque which causes 
the motor to speed up until the counter E. M. F. attains a value so 
as to reduce the current to the value necessary to supply the required 
torque. 

Speed Control. — It has been shown that the speed of a shunt 
motor varies very little with changes of load from zero to full load, 
and when used for power where a varying speed is required, special 
arrangements are necessary. 

Armature Resistance Method. — When the load on the motor is 
constant, its speed may be controlled by inserting resistance in series 
with the armature. When the resistance of the armature is large 
or when a large resistance is in series with the armature, equation 
(6) shows, that for a loaded motor, the large C a necessary to pro- 
duce the required torque can only be obtained by a large value of 
the numerator, @ — nZN, and this can only be obtained by a large 
change in n in order that nZN can be considerably less than (?. 

On zero or light load, C a is small, so the speed is not much 
affected by having r a , or r a + the resistance, large. This con- 
sideration shows that the change in speed for loads over a wide 



268 Naval Electricians' Text Book 

range cannot be satisfactorily effected by changes in armature re- 
sistance, but for loaded motors it is effective. 

Field Resistance Method. — Equation (7) shows the zero load, 
and consequently full load to practically the same extent, may be 
changed by varying N. This is effected by means of a resistance in 
series with the shunt winding, which can be increased or decreased, 
thus decreasing or increasing the field current and N pro- 
portionately. 

The regulation by this means is limited, for the field cannot be 
increased above its saturation point, nor can it be decreased below 
a certain value, for the torque decreases with the field, and the 
magnetic reactions in the armature may overpower the weakened 
field. 

Other methods of control applicable to motors in general will be 
discussed later under the head of Motor Control. 

Series Motors. 

With this form of motor the field varies with the strength of 
current. If the load on a series motor is reduced, the increase of 
torque, or rather the excess, causes the speed to increase, thereby 
diminishing the current and weakening the field, again causing 
the speed to increase to a greater extent to increase the counter 
E. M. F., than in the case of the shunt motor. If the load is in- 
creased there is a deficit of torque, the speed falls, the current 
increases, thereby increasing the field so that the speed must de- 
crease considerably in order to reduce the counter E. M. F. to the 
proper amount. The speed, therefore, of the series motor varies 
considerably with the changes in load, and on this account is used 
on hoists, such as ash hoists, boat hoists, ammunition hoists, or 
where there are wanted both variations in the load and speed. 

The field of the series motor may be varied in exactly the same 
way as the E. M. F. in a series generator is varied by cutting out 
some of the series turns, or introducing a resistance in parallel with 
the series windings. 

One disadvantage of the series motor is that if by any chance 
all the load is thrown off, the required current is very small, and 
so weakens the field that it requires a very high speed to generate 






Theory of Motors axd Motor Control 269 

the proper counter E. M. F. and the speed may become so great as 
to rack the armature to pieces. An advantage of this motor is that 
it allows a strong current and consequently strong torque at start- 
ing, a very important element in getting heavy weights such as 
anchors, or boats, or turrets started. 

Regulation. — In certain cases, a good method of regulating these 
motors is to regulate the E. M. F. of the supplying generator, start- 
ing with a high E. M. F. where great torque is required, and cutting 
it down as the speed rises. This is not as wasteful as introducing a 
resistance in the main circuit, and keeping the supplying E. M. F. 
constant as is sometimes done. 

Compound Motors. 

As the object of compound generators is to produce a constant 
potential at all external loads, so the object of compound or dif- 
ferentially wound motors is to produce constant speed under all 
external loads. This problem is solved by building motors with 
a compound field consisting of the ordinary windings of the shunt 
motor with a few turns of series windings, so arranged that they 
are opposed to each other, one tending to magnetize and the other 
to demagnetize. The effect of this method of winding can be illus- 
trated by taking the case of a shunt motor with a constant potential, 
running at a constant speed. If the load is suddenly reduced, the 
excess of torque causes the motor to increase in speed which will 
increase the counter E. M. F. and cut down the armature current. 
This would tend to reduce the torque, but on account of the internal 
resistance of the armature, all of the current is not available for 
this purpose so the speed will not fall to exactly what it was before. 
Xow in the case of the compound motor, at all times there is a con- 
stant demagnetizing effect due to the series windings, and as the 
current is decreased, as the armature speeds up, this demagnetizing 
effect is lessened, or the field strengthened, so the required counter 
E. M. F. is obtained without any increase of speed; or, in other 
words, it remains constant. It is evident then there should only be 
enough series turns to make up for the energy lost in overcoming 
the motor resistances, friction and core losses. 

The speed at which the compound motor runs should be the 



270 Naval Electricians' Text Book 

same speed as that, if used as a generator, it would yield an E. M. F. 
equal to that of the supplying source. At this speed it should run 
so fast as to reduce the armature current to a minimum. By 
making the shunt field strong enough the required speed can be 
made as low as desired. 

If the speed is to be constant, the counter E. M. F. must be 
constant, and as the load changes, the torque and consequently the 
armature current changes, so the counter E. M. F. can only be 
kept constant by changes in the magnetic field which is accom- 
plished by the series turns, the field diminishing as the current 
increases and vice versa. 

It is usual in starting differently wound motors to have an 
arrangement for keeping the series turns out of circuit until the 
motor has speeded up, for if the series and shunt windings are 
properly proportioned to govern exactly, there might not be any 
resulting magnetism, or if one overbalanced the other, the motor 
might start to run the wrong way. 

Other Method of Compounding. — One other method of com- 
pounding has been to wind two separate circuits on the armature, 
one to receive the supplied current, and the other acting as a gen- 
erator, inducing its own current and which is connected to the 
series windings. As the armature speeds up, the induced current 
becomes greater and tends to increase the field, so the counter 
E. M. F. is obtained by a lower speed. If the armature slows 
down, the induced current is lessened, the field magnetism is low- 
ered, and a higher speed is necessary to produce the counter E. M. F. 

Generators as Motors. 

Generators designed for continuous currents may be used, in 
all cases, as motors with some slight changes. A series generator 
used as a motor will run in the opposite direction to that in which 
it must be driven in order to build up as a generator. 

Fig. Ill shows a diagrammatical sketch of a series generator 
and series motor. 

In Fig. Ill the left-hand figure represents a series generator, 
the curved arrow representing the direction of rotation of the 
. armature, with the resulting current in the external circuit and 



Theory of Motors axd Motor Coxtrol 271 

through the armature represented by the arrows in those parts. 
The arrow A represents the resultant mechanical force between the 
field and armature current and in the generator the counter force 
that the power driving the armature overcomes. 

With given connections of field to the armature, the relative 
direction of current through field and armature is the same whether 
used as a generator or motor, and consequently there is no change 
in the mechanical force with which the field acts on the armature 
conductors. In the generator the power overcomes this force, but 
in the motor, it produces the motion, so consequently the force 
that has been overcome in the generator acts to produce opposite 
rotation when used as a motor. 

It is immaterial which way the current flows when used as a 
motor, for the reversal of the supply current simply reverses both 



MAM i — AWV 





Fig. 111. — Series Generator and Motor. 

the direction in the armature and in the field and does not change 
the relative directions, so there is no change in the force exerted 
by the field on the conductors. 

To reverse the direction of the series motor, the armature current 
must be reversed without shifting the direction of the field current, 
by shifting the connections to the brushes. 

A shunt generator with given connections of field to armature 
will run as a motor in the same direction that it must be run to 
build up as a generator. 

Fig. 112 shows a diagrammatical sketch of a shunt generator 
and shunt motor. 

In Fig. 112 the left-hand figure represents a shunt generator, 
the curved arrow representing the direction of rotation of the 
armature, with the resulting current in the various parts repre- 
sented by straight arrows. The arrow A represents the resultant 



272 Naval Electricians' Text Book 

mechanical force between the field and armature current and in the 
generator, the counter force that the power driving the armature 
overcomes. 

In the generator, it is noticed that the current in the armature 
and in the field are opposed to one another, while in the motor, 
they are in the same direction. Consequently, in the motor, there 
is a relative change in the direction of the armature and field cur- 
rents and also there is a change in the mechanical force that repre- 
sents the resultant action of the field on the armature conductors. 
In the generator this force is overcome by the power driving the 
armature, and the force being reversed, now drives the armature of 
the motor in the same direction. 

In this case, also, it is immaterial which way the current flows 
in the motor circuit for a given connection to the brushes ; for the 





Fig. 112. — Shunt Generator and Motor. 

reversal of the supply current simply reverses the current in both 
armature and field without producing any relative change, so there 
is the same change in the mechanical force, which being Opposite to 
that of the generator, causes the motor to revolve in the same 
direction. 

To reverse the direction of rotation of the shunt motor, either 
the current through the armature or through the field should be 
reversed, but not both. 

Compound Generator. — A compound-wound generator when run 
as a motor will run in either direction, depending on the relative 
strength of the two fields. 

Efficiencies of Motors. 

As in the case of generators, there are three efficiencies represent- 
ing the relation between the energy furnished tho motor, the energy 



Theory of Motors axd Motor Control 273 

absorbed by the motor, and the energy supplied by the motor. Of 
these, the first two are electrical quantities and the third mechan- 
ical, all of which must be expressed in the same units either 
electrical or mechanical to obtain a proper percentage of efficiency. 

Gross Efficiency. — This is a term given to express the relation 
between the power actually absorbed by the motor and the total 
power supplied to the motor at the terminals. As in the notation 
previously used, if (£ is the difference of potential at the motor 
terminals, and C, the current flowing in the supplying mains, then 
the total energy in watts supplied to the motor is ©0. If E repre- 
sents the counter E. M. F. and C a the armature current, then the 
total power in watts absorbed by the motor is EC a , and the gross 
efficiency would be EC a -f- @C. In the series motor C a = C, and 
in the shunt motor C a = C — C s , the latter term representing the 
shunt current. 

Both @ and C can be directly measured by connecting a volt- 
meter at the terminals and connecting an ammeter in series with 
the supply mains. The difference between Q and E represents the 
volts lost in the armature, and as in the case of a shunt generator 
is equal to C a r a , or © — E = c a r a . C s is calculated by knowing 
the difference of potential at the shunt terminals and the resistance 
of the shunt, for (£ = C s r s . Thus knowing C and C s , C a is known, 
or it might be measured directly by connecting an ammeter in the 
armature circuit. Knowing C a , the lost volts are known, which 
subtracted from @ will give E. The greater E is the greater the 
gross efficiency. 

In the case of motors, the gross efficiency is really the efficiency 
of the motor per se, being entirely a relation of electrical quanti- 
ties and corresponds to the electrical efficiency of a generator. This 
efficiency can be as high as it is possible to make E by reducing all 
core and friction losses and by making the internal resistance as 
small as possible. 

Law of Maximum Activity. — There is a law of maximum activity 
which was confounded with the law of maximum efficiency in the 
early days when the working of motors was not as well understood 
as at present. The power utilized in a motor is the difference 



274 Naval Electricians' Text Book 

between the total power supplied and the power lost in overcoming 
the internal resistances, or the heat loss, the C 2 R loss. , 

If w is the power utilized, 

w = W — C 2 R. 

When w is a maximum, C has a value equal to one-half the value 
it would have if the motor was at rest, for 

dw = d — 2CB, 

which is a maximum when dw = 0, or 

@ = 2CB and C = iJ®. 
2 i? 

-g equals the current when motor is at rest, so the maximum work 

is done when the motor runs at such a speed that the armature cur- 
rent is reduced to one-half what it would be if the motor is at rest. 
This means that when the motor is doing work at its greatest 
activity its efficiency is only 50 per cent for 

or 

%E—% 

or, as before, the efficiency is-^- = -J = 50 per cent. 

Electrical Efficiency. — This is a term that represents the relation 
between the total power absorbed by the motor and the total power 
given out by the motor, the first being an electrical quantity and 
the second mechanical. The first term is the product of E and Ca, 
and it has been explained how they are obtained. The mechanical 
power developed at the pulley of the armature motor is the product 
of the torque developed and the radius through which it acts, in 
precisely the same way that the power exerted by the current in the 
armature is the product of its torque and the radius of the arma- 
ture. If the torque is expressed in pounds force and the radius in 
feet, the work is expressed in ft.-lbs. which may be reduced to 
horse-power. 

The torque can be measured in several ways; by finding the 
difference in tension of the sides of a belt that runs on the arma- 



Theory of Motors and Motor Control 275 

ture pulley, or by means of the Prony brake, which is simply an 
arrangement for measuring the friction exerted between the pulley 
and an arm connected to a scale which will measure the friction 
absorbed at any given speed. Still another method is by means of 
the Brackett cradle, in which the motor is mounted in a cradle and 
accurately balanced. When running with any load, the tendency 
of the field frame to turn around the armature axis by which it is 
balanced is measured as so many ft.-lbs., by finding how many 
pounds weight at a certain distance will balance this tendency, or 
the motor measures its own output. 

Net Efficiency. — This is a term that expresses the relation be- 
tween the total mechanical power produced by the motor and the 
total electrical power supplied, both of course being expressed in the 
same units. It has been explained how both of these factors are 
found and the net efficiency is simply the quotient obtained by 
dividing one by the other, and it is also numerically equal to the 
product of the other two efficiencies. The power supplied is called 
the input and that obtained the output, and the differences between 
these quantities represent the losses in the motor. 

Motor Losses. 

As stated above the total loss in a motor is represented by the 
difference between the input and the output and this loss is made 
up of the same elements as in the case of generators, part being 
electrical and part being mechanical losses^ and made up of me- 
chanical friction in the bearings, friction between the brushes and 
commutator, air friction of the revolving armature, core losses due 
to eddy currents and hysteresis, frame losses, due to eddy currents 
in the pole pieces and the copper losses in the field windings and 
armature conductors. 

The difference between the total power supplied and the total 
power absorbed is represented by the heat losses in the field and 
armature, or is the power that is lost in overcoming the resistances 
of those parts. In a shunt motor, the field loss would be C 2 s r s 
watts and in the armature C 2 a r a watts. The total core and friction 
losses taken together is equal to the sum of all the losses minus the 
sum of the field and armature losses, and is also equal to the differ- 



276 Naval Electricians' Text Book 

ence between the total power absorbed by the motor and the power 
developed by it. 

Since the speed of a shunt motor is practically constant at all 
loads, the losses are practically constant at all loads, and they can 
be very approximately calculated by finding what current will run 
the motor free at its given speed. There is no output and the input 
represents the mechanical and core losses and the loss in the field, 
as the armature loss will be so small that it may be neglected. 

As an example, suppose a shunt motor requires a current of 
8 amperes at 80 volts when running free at 1500 revolutions. 
Armature resistance .04 ohm and shunt resistance 20 ohms. 

Meld current or C s = |£ = 4, and C a = C — C s — 8 — 4 = 4. 
/c0 

Loss in field C 2 s r s = 4 X 4 X 20 = 320 watts. 

Loss in armature C 2 a r a = 4 X 4 X -04 = .64 watts neglected. 

Total input @C = 80 X 8 = 640 watts. 

Mechanical and core losses = 640 — 320 = 320 watts. 

Now suppose the net efficiency was wanted when the motor was 
working with a current of 36 amperes. 

As before C s — |£= 4 and C a = 36 — 4 = 32. 

Loss in field C 2 s r s = 4 X 4 X 20 = 320 watts. 

Loss in armature = 32 X 32 X .04 = 41 " 

Mechanical and core losses (as above) = 320 " 

Total losses =681 " 

This leaves (80 X 36) — 681 = 2199 " as the output, 

or the efficiency = = 76.4 per cent. 

As a matter of experiment this motor when absorbing 36 amperes 
and 80 volts, showed 2.97 H. P. at the pulley, or 2.97 X 746 = 2214 

2214 
watts, which would give an efficiency = oqqo — 76.8 per cent, 

showing that the mechanical and core losses calculated when run- 
ning free must have remained constant under the increased load 
which was great enough to require 36 amperes. 

In order to separate the total friction and core losses, that is, 
separate the loss due to mechanical friction, that due to eddy cur- 



Theory of Motors and Motor Control 277 

rents, and that due to hysteresis, it becomes necessary to make other 
connections and make observations at different speeds, as we saw 
under generators that eddy currents vary with the square of the 
speed, and hysteresis directly as the speed. An ordinary way of 
doing this is to separately excite the field magnets and to note the 
number of volts and amperes absorbed when the motor is running 
at different speeds with no load. Using the amperes as ordinates 
and the volts as abscissae, curves can be plotted, the ordinates of 
which, being proportional to the current, will represent the losses 
at that current. If the curve is a straight line parallel to the axis 
of volts, all the losses are directly proportional to the current or 
there is no loss due to eddy currents, but if the curve makes an 
angle with the axis of volts, the increase of ordinates over those 
due to friction and hysteresis represent losses due to the eddy 
currents. 

To further separate the friction losses from hysteresis loss the 
armature should be coupled direct to another similar machine run- 
ning without a field excitation, when the increase of current neces- 
sary to run this second machine will be a measure of the frictional 
loss, which deduced from the other total loss independent of the 
eddy loss, will give the hysteresis loss. 

Motor Control. 

By this term is meant the operation of devices introduced be- 
tween the supply lines and a motor by which the motor is stopped or 
started, and by which the direction and speed of the armature is 
controlled. The systems of control used in motors on ships of the 
navy are those generally known as the Automatic Eheo static sys- 
tem, the Leonard system, the Day system, and the Panel system. 
The devices by which these systems are put in operation are gen- 
erally known as Starting Panels or Controllers, which contain the 
necessary switches, fuses, resistances, etc., for controlling the 
current. 

Operation of Motors. 

If the armature of a motor at rest was suddenly connected to a 
source of supply of current, an abnormally large current would flow 



278 



Xaval Electricians' Text Book 



through the armature owing to its low resistance. This arises from, 
the fact that as the armature is at rest, it cannot develop any- 
counter E. M, F. to reduce the incoming current. It does, however, 
do so the moment it commences to revolve and as its speed increases, 
counter E. M. F. is generated to sufficiently reduce the current to 
its normal flowx 

To prevent this first sudden inrush of current, it is usual in all 
forms of motors that are to be used as motors alone to introduce a 
resistance in series with the armature, so that when the circuit is 
first established only sufficient current flows through the armature 
to produce sufficient torque to cause revolution of the armature. 



+ 




AAA/WW 



wvwv- 

Ht R 



Fig. 113. — Control of Series Motor. 



As soon as the armature starts to revolve and counter E. M. F. is 
generated, this reduces the supply current, so some of the resistance 
may be cut out which will allow more current to flow and greater 
torque to be produced. As the armature speeds up, the resistance 
is gradually cut out until the armature terminals are directly con- 
nected to the full voltage of the supplying mains and the armature 
is running at its full speed. 

It has been previously shown that in order to reverse the direc- 
tion of revolution of the armature that either the field current or the 
armature current must be reversed, out not both. In some cases 
of reversal the armature current is reversed and this might be con- 
sidered the ordinary way, but in others to be mentioned later, the 
field current is reversed. 



Theory of Motors axd Motor Control 



279 



Rheostatic Control. 

Series Motors. — This form of control is illustrated in the ele- 
mentary diagram shown in Fig. 113. 

To Start. — The field coil F is in series with the armature through 
the rheostat R and connected to the supply lines marked -J- and — 
through the reversing switch RS. When the switch RS is first 
closed, all the resistance R is in circuit, but as the armature M com- 
mences to turn and develop counter E. M. F. the resistance is 
gradually cut out until the arm H rests on the last contact of the 
resistance when the armature receives the full line voltage. This 
constitutes the rheostatic control for starting. In actual starting 



^fc 



R S 



^ 



WVWW- 

Ht R 



Fig. 114.— Control of Shunt Motor. 



devices for series motors, the armature current and field current are 
connected to the mains at the same time by means of the switch or 
controller, after which the resistance in the field is gradually 
cut out. 

To Stop. — To stop it is only necessary to reverse the operation 
of starting, moving the rheostat arm over the contact points until 
the last is reached when the field and armature current is broken 
at the same time by the switch. It is well to make the motions 
quickly to avoid the sparking that might occur when the circuits 
are broken. 

To Reverse. — To reverse the direction of rotation of the armature 
it is only necessary to move the switch S to the other contact points 
shown, when an inspection will show that though the current 
through the field is in the same direction as before the direction 



280 Naval Electricians' Text Book 

through the armature has been reversed. To do this, however, the 
armature should first be brought to rest and with all the resistance 
in circuit. 

Shunt Motors. — The control for shunt motors is illustrated in 
the elementary diagram shown in Fig. 114. 

In addition to the reversing switch, which in the case of series 
motor also acts as a starting switch, a shunt motor should be pro- 
vided with a double-pole switch in the main line and the usual 
starting resistance. 

To Start. — Close the double-pole switch L8 which sends current 
through the shunt coils F and excites them at the constant potential 
of the line marked -|- and — , and it is important to note that in 
all cases the motor field is energized before any voltage is applied 
to the armature. The switch RS should then be closed one way or 
the other, sending current through the resistance R in series with 
the motor armature M. The resistance R is then gradually cut out 
as in the case of the series motor and the armature brought to 
speed. 

To Stop. — The line switch LS should be opened, first cutting off 
the armature current, and as soon as the armature is at rest, the 
arm H should be run quickly back throwing in all resistance ready 
for starting again. 

If the rheostat arm is moved first there is likely to be bad spark- 
ing or flashing when the off position is reached and when the line 
switch is opened there is apt to be a long arc endangering the field 
coil insulation. 

Cause of Flashing. — This is caused by the self-induced current 
in the field as the field current commences to weaken. The in- 
duced current tends to keep up the field current and on account of 
the number of turns in the field winding and the iron core, the 
momentary current has a high E. M. F. which manifests itself when 
the circuit is broken by the spark, a manifestation of the tendency 
of the induced current to keep on flowing. 

To Reverse. — When the motor is at rest, it is only necessary to 
shift the reversing switch RS to its other contacts, and it will be 
then seen that, as the field connections are beyond this switch, the 



Theory of Motors and Motor Control 



281 



current through it will be as before, while the current through the 
armature is reversed. 

Compound or Differential Motors. — These are started and stopped 
in exactly the same way shunt motors are, it being usually arranged 
that the compound windings (series) are not thrown in circuit until 
all the starting resistance is cut out and the motor is running at 
its full normal speed. 




Fig. 115. — Ward Leonard System of Control. 



The Leonard Control. 

In the rheostatic method of control it is seen that in starting 
motors only a small portion of the line voltage is applied to the 
armature terminals at first, being gradually increased as the motor 
gets up its speed. It has also been shown that this is effected by 
means of a resistance in series with the armature, which with the 
armature resistance is sufficient to reduce the first current to about 
1-J times the full-load current. Thus, about half the voltage ap- 
plied is used up in this resistance, being equal to the current flowing 
times the resistance, and is dissipated as heat. This is a great loss 
in economy and the object of the Leonard control is to generate only 



282 Naval Electricians' Text Book 

enough voltage to produce the desired current without the inter- 
vention of the wasteful resistance. 

This system of control finds its greatest application to ship's 
motors in turret-turning and gun-elevating motors, and will be 
fully described later; at this time only the elementary principles 
being explained. 

The elementary diagram illustrating this method of control is 
shown in Fig. 115. 

In figure, D is a generator armature directly connected to the 
motor armature M through the reversing switch RS, DF is the 
generator field, and MF the motor field. The supply mains + and 
— are energized to full potential by some .other source of power. 

As long as the generator field is broken by the arm H being off 
the rheostat R, the field of the generator is not energized and there 
is no voltage generated in it, though the motor field is fully excited 
from the mains. 

When H first makes contact with R a small current then flows 
through the generator field and the generator armature revolving in 
this field generates a small difference of potential which is impressed 
on the motor terminals. As soon as this voltage is sufficient to 
generate enough current to produce the necessary torque the motor 
armature commences to turn, and will attain a speed proportional 
to the volts impressed on its terminals and which in turn is the 
full amount generated by the generator. 

By cutting out the resistance in R, the voltage of D gradually 
increases, the voltage at M increases the same, and the motor arma- 
ture gradually speeds up. 

By this method of control there is no wasteful energy m motor 
armature resistances and the changes of speed are gradual and can 
be absolutely controlled by the generator field rheostat from start up 
to the maximum speed. 

The direction of rotation of the motor armature can be changed 
by shifting the reversing switch R8. 

To slow the speed it is only necessary to cut in resistance in R 
and if this is done quickly the voltage at the terminals of D may 
fall much below that of M for the instant, in which case M will 



Theory of Motors and Motor Control 283 

now tend to act as a generator and will generate large currents, 
quickly slowing it down until the voltage reaches that of D. 

If from any cause the voltage of D is cut off, and the load on 
M tends to rotate it, the motor will then act as a generator short- 
circuited at its terminals and the large currents generated will act 
as a counter drag on its conductors and quickly bring it to rest. 

The Day Control. 

This system of control finds its greatest application in hoisting 
work, in which it is necessary to have the hoisting mechanism 
overhaul itself as quickly as possible as well as to have its speed 
absolutely controlled. When a weight is to be lowered, it may not 
exert sufficient force to overcome the friction of the moving parts, 
in which case it is necessary to have a motor to start it, or it may 
fall by its own weight, in which case it will cause the motor to act 
as a generator, and the braking action of the motor armature in con- 
trolling the speed in lowering constitutes the chief feature of the 
Day control. 

For hoisting it is usual to have the resistance in series with the 
armature both for starting and for speed control, but for lowering 
a load or carrying very light loads a different combination is made, 
so that the rheostat to which the controlling switch is connected, 
instead of being in series with the armature and gradually short- 
circuited as the armature is brought up 
to speed is connected across the line in 
parallel with the armature. 

The elementary connections are shown 
in Fig. 116. 

By this arrangement a small amount Laaaaaaa AAA A 

of current is taken from the line through JH 

the rheostat R while the armature is 

being operated, in addition to the cur- " 'C M J/" 

rent taken or given out by the armature FlG> 116 _ Day System of 

itself, according as it is acting as a motor Control. 

or as a generator. 

On the first contact of the resistance, the rheostat is connected 
across the line and the armature is in parallel with a very small 
portion of the rheostat. 



284 Naval Electricians' Text Book 

The portion of the rheostat between the armature terminals may 
be considered as being in parallel with the armature as far as cur- 
rent taken from the line is concerned, and in series with the arma- 
ture as regards current produced by the armature itself. 

If on lowering, and on the first contact of the resistance, the 
load does not start, the motor armature will receive a small current 
from the line through the rheostat and proportional to the differ- 
ence of potential between the points on the resistance to which it is 
connected. If the armature does not now start, throw in more 
resistance in parallel with the armature, shown in Fig. 116, by 
moving H more to the left. This will allow more current to pass 
through the rheostat into the armature, or the difference of poten- 
tial between the terminals will now be greater. 

If, however, in the first instance, the load was sufficient to over- 
haul itself, it would cause the motor to act as a generator and cur- 
rent would be given out by the armature through the small portion 
of the resistance with which it is now considered as being in series. 
The load still overhauling, any further movement of H to the left 
w T ould cause the motor to move faster, as it is now generating cur- 
rent through an increasing resistance. To slow in this case, it is 
only necessary to move the contact arm to the right, when the motor 
is generating current through a smaller resistance, when larger 
currents would flow, and as this energy is brought into existence 
by the falling load it would gradually slow down, until when the 
armature circuit is short-circuited, the powerful currents induced 
would act as a counter torque and bring the weight to rest. 

Moving the contact arm to the left, the armature will be grad- 
ually brought to full speed, whether the motor is acting as a 
generator as has been shown, or whether it is taking current from 
the line. 

In this way the speed can be controlled no matter whether the 
motor is really lowering the load or whether the load is driving 
the motor. 

In the ordinary rheostatic control with the resistance in series 
with the armature, more resistance turned into the circuit will 
cause the armature to run faster when it is driven by its load and 
there is no way of reducing its speed below its full-load speed. 



Theory of Motors and Motor Coxtrol 285 

Panel Control. 

The systems of control previously discussed have had to do with 
the different means of starting motors by means of variable resist- 
ances in series or in ]3arallel with the main current, and the varia- 
tion in speed caused by changes in the voltage impressed on the 
motor terminals by changes in this resistance. 

In the Panel control, the usual starting resistance is used, but 
changes in speed are caused by changes in the field excitation. 

Speed Regulation by Change of Field Excitation. 

Suppose a motor with constant voltage applied to its terminals 
to run with a constant load. The motor will run at constant 
speed, the current being just sufficient to overcome all losses and 
the resistance due to its load. If the field current is lessened, the 
counter E. M. F. would decrease in the same proportion if the 
speed remained as before. This would allow a greater current to 
flow through the armature and the increased power due to the 
increased current would cause the motor to run faster, until the 
counter E. M. F. had increased to such a value that the power 
absorbed by the motor was sufficient to overcome the resistance of 
the load at the new speed. 

This shows a decrease in the field excitation, produces an increase 
in the speed, and vice versa. 

The regulation of speed in a shunt motor is easily attained by 
connecting a variable resistance in series with the shunt winding, 
and as the current is small, the waste of power, or heat loss, is not 
great. In many cases variation in speed is attained by putting 
resistance in series with the armature. 

In a series motor, the field regulation is more economically 
carried out by connecting a variable resistance in a branch circuit 
in parallel with the series winding. The current round the series 
coils is then decreased by decreasing the variable resistance in the 
branch circuit, causing more current to pass through this branch 
resistance instead of around the series windings. 



286 Naval Electricians' Text Book 

Problems on Motors. 
1. A shunt motor has an armature resistance of .04 ohm and a 
shunt resistance of 20 ohms. A current of 36 amperes is supplied at an 
E. M. F. of 80 volts; the armature makes 1500 revs, a minute, giving a 
tangential pull of 44 lbs. at the surface of a pulley whose circumference 
is 18". Find the loss by heat in the armature and field, the counter 
E. M. F., the current in the armature and shunt, and the efficiency 
(net). 

® = C s r s C = {So = 4 C a = 36-4 = 32, 

Q=zE + C a r a or # = 80— (32 X .04) =78.72. 

Watts lost in field = (£(7 S =80 X 4 = 320 
Watts lost in arm. = C 2 a r a =~32 2 X .04 = 40.96 



Total loss = 360.96 watts. 

Watts supplied = gC = 80 X 36 = 2880 watts, 
Watts developed = EC a = 78.72 X 32 = 2519.04 " 
or loss = 360.96 

1 500 y ^ y 44 
H. P. avail. = 2 X 33000 ~ 8 or 8 X 746 = 2238 watts ' 

2238 

Net efl. = 2885 =7W. 

2. In a shunt motor, resistance of field coils 50 ohms, of armature 
.2 ohm, total current entering 25 amperes, difference of potential 100 
volts, H. P. as indicated by dynamometer 2.75, find the electrical, gross, 
and mechanical efficiencies. Ans. Gross eff. = 87.7$. 

Elec. eff. =93.5$. 

Mechanical eff. =82$. 

3. A shunt motor has a field resistance of 33% ohms, and an armature 
resistance of .06 ohm. The difference of potential is 100 volts and the 
current 48 amperes. The radius of the pulley is 3". The difference of 
the weights of a flexible band dynamometer is 63 lbs. and the number 
of revolutions is 1800 per minute. Required, the gross, electrical and 
commercial efficiencies, and the loss in heating the coils. 

e ioo 

C s =— — ggy- = 3 amperes, 

C a = 48 — 3 = 45 ® — E = C a r a, 

or E = 100 — 45 X .06 = 97.3. 

Watts supplied = ©C = 100 X 48 = 4800, 
Watts utilized =#C a = 97.3 X 45 = 4378.5 



Watts lost in heating 421.5. 

Total output = wT where w is the angular velocity and T the torque 
in ft.-lbs. a = 27m. 

o)T in ft.-lbs. = 2irnT X 1.356 in watts, 



Theory of Motors and Motor Control 287 

33000 
for 1 H. P. =746 watts and 1 ft.-lb. per sec. — 6Q =550 ft.-lbs. 

746 
or 1 ft.-lb. per sec. = >_.-= 1.356 watts. 

22 1 son 
output in watts = 2 X -j X ^ X 63 X i X 1.356 = 4027.4. 

Gross eff. = *|™ = 91.22* Else eff. = ™™ = »*. 

4027 3 
Commercial eff. = ,»q'q = 83. 9#. 

4. An electric motor, shunt, has an armature resistance of .055 ohm 
and field resistance of 32 ohms. When making 1400 revs, per minute 
the tangential pull on a pulley 7.6 cm. radius is 25 kilos. The current 
supplied to the motor at a voltage of 105 is 35 amperes. Calculate the 
counter E. M. F., the heating effect, and the gross and mechanical effi- 
ciencies. 

Output = ^ 07 watts, where T is the torque expressed in ergs, 1 watt 

being equal to 10 7 ergs per sec, or output in watts 

9V 22 ^ # 1400 w 7.6 X 25 X 1000 X 981 _ 
- 2X T x_ 60~ X W —1(66.1 

7.6 X 25000 = gr. cm. which multiplied by 981 gives ergs. 
c — ®ZZ^ or E = © — C a r a = 105 — 31.72 X .055 = 103.255, 
@ = C s r s C s = ~ = 3.28 C a = 35 — 3.28 = 31.72, 



ec a = 105 X 35 =3675 watts, 
EC a = 103.26 X 31.72 = 3275 " 



Heating effect 400 " 

Gross eff. = ||^| = 89.125^. Mechanical eff. = ^|^ = 74.38^. 

5. A Thompson-Houston motor has an armature resistance of .06 
ohm and field resistance of 33% ohms. While absorbing a current of 
32 amperes at 102 volts, the armature made 1350 revs, per minute with 
a tangential pull of 60 lbs. on a pulley 6 inches in diameter. Calculate 
the heating effect and the mechanical energy delivered and the electrical 
energy supplied. 

Ans. Heating effect = 362.36 watts. 

Elec. energy supplied =3264.00 
Mech. energy delivered = 2876.6 

6. A shunt motor connected to 110-volt mains, when unloaded, takes 
3 amperes in the armature and runs at a speed of 997 revs, per minute. 
The armature resistance is .11 ohm. Calculate the resistance that must 
be connected in series with the armature to reduce its speed to 800 revs, 
per minute when the armature current is 50 amperes. Ans. .33 ohm. 



288 Naval Electricians' Text Book 

7. In the preceding example, the shunt current was 2.6 amperes and 
at full load, 50 amperes, the actual speed was 980 revs, per minute. 
This machine is now driven as a generator at a speed of 980 revs, per 
minute and the field rheostat is adjusted to give the same field current 
as before. Find the" terminal voltage of the generator when the arma- 
ture current is 50 amperes, and the difference in the resistance of the 
field (field and rheostat) in the two cases when acting as a generator 
and as a motor. 

If the field current remains the same and the speed as a motor and 
generator constant, the counter E. M. F. of the motor will be equal to 
the total E. M. F. as a generator. 

Counter E. M. F. — 110 — C a r a = HO — 50 X .11 = 104.5 
e as generator = E — C a r a = 104.5 X 50 X .11 = 99 volts. 

Resistance of field and rheostat as motor = -Twf — 42.3 ohms. 

99 
Resistance of field and rheostat as generator = -n-g — 38.1 ohms. 

8. A 110-volt shunt motor has a speed of 1200 revs, per minute. The 
resistance of the shunt field is 110 ohms. The constant stray loss due 
to friction, eddy currents, etc., is 250 watts. The armature resistance 
is .4 ohm. Find the value of the armature current for which the effi- 
ciency is a maximum and find this maximum efficiency. 

Note. — The maximum efficiency occurs when the variable loss is 
equal to the constant loss. Ans. 30 amperes. 

78.9$. 

9. Assuming that the armature flux of example 6 is constant at all 
loads, find the value of the counter E. M. F. and speed for which the 
output is a maximum; the value of the output and the efficiency. The 
shunt current is 2.6 amperes. 

Note. — Maximum output results when the motor has such a speed 
that the current is reduced to half what it would be if at rest. 

110 
At rest C a = -jy = 1000 amperes, 



for maximum output C a 


1000 


500 


amperes, 


® — E- 


-CaXa, or E = 


: 110 —500 X .11 = 55 volts, 




nZN 
E — 1Q8 


110 — 3 X 


: .11: 


997#Z 
10 s 




NZ 

io 8 " — 


109.67 
"997 ~ 


.11, 




110 — 50 X 


nNZ „ 


.11, or 


n = 


^-=500 R. 


Total input = 


: 110 X 502.6 = 55286 watts. 







Theory of Motors and Motor Control 289 

When unloaded, power absorbed = C a E = 3 X 109.67 = 329 watts, or 
329 watts are expended without doing work. 

Total output = G a E — 329 = 500 X 55 — 329 = 27.171 watts. 

27 171 

Efl - = 55:286 = 49 - 2 *- 

10. A motor generator is built up of a motor and generator mounted 
on a common shaft. Characteristics of motor: drum wound armature 
with 65 complete coils, armature flux 8,000,000 lines; difference of 
potential at terminals 110 volts; resistance of armature .1 ohm, of 
shunt winding 44 ohms, external current 62.5 amperes. Characteristics 
of generator: long shunt compound wound; ring armature with 120 
coils; armature flux 9,200,000 lines; resistance of armature .09 ohm, 
of series winding .11 ohm, of shunt winding 50 ohms; total external 
resistance 2 ohms. Calculate the current the generator will deliver. 

Ans. 50 amperes. 



CHAPTEE XVI. 
SERVICE MOTORS. 

At the present time nearly all the power used on board naval 
vessels, with the exception of the power for propulsion, for capstans 
and steering engines, is furnished by electric currents through the 
medium of electric motors. Electric power is used for turret train- 
ing, gun elevating, ammunition hoists of all kinds, boat hoists, deck 
winches, coal hoists, ash hoists, air compressors, water-tight doors 
and hatches, work shop machines, ventilating fans, blowers, and 
miscellaneous uses, such as operating laundry machines, printing 
presses, meat choppers, dough mixers, ice-cream freezers, potato 
peelers, etc. 

Motors for operating the various machines and devices are located 
at different parts of the ship, all subject to different conditions of 
wear and use, some on deck where they are liable to be drenched 
with salt water and exposed to rain, as boat hoists and winches, be- 
sides exposure to coal dust when coaling; some subject to flying 
spray at times, as the turret motors and gun-mechanism motors. 
Others are located in the lower parts of the ship subject to great 
heat and in out of the way places, where they can get little care, as 
ventilating fans in air ducts and trunks. Some are in the fire- 
rooms, as the forced draft blowers, subject at all times to great heat 
and flying coal dust. 

Some motors are constantly used, as the ventilating fans, some 
not so often as fans for forced draft, and others intermittently as 
boat, and other hoists and deck winches. Some run continuously, 
as fans, without change of speed or -load, others, as turret motors, 
are continually starting, stopping, reversing, and changing in speed 
and load. Each class of motor then must be designed for the par- 
ticular work that it is required to do and only a few requirements 
are applicable to all. It is very evident that they should be of 
inclosed water-tight and dust-tight type, of particularly strong 



Service Motors 291 

mechanical construction so as to be able to stand hard usage, and 
strong electrically to stand for a short time any dangerous over- 
loading. As far as possible all should have automatic or self- 
oiling bearings and the brushes should be fixed and fitted so as not 
to jump away from the commutator, and should be independent of 
care and attention. The motors should be of such good mechanical 
and electrical construction that the only care necessary should be an 
occasional trimming of the brushes and a look at the commutator, 
and the precaution taken of seeing the oil cups filled. The starting, 
stopping, and reversing gear should be of the simplest description 
so that any one could be entrusted to run the motor. 

General Specifications for all Motors. 

Motors installed on board vessels of the navy are furnished under 
different specifications, but all conform to general requirements, 
and as a general guide to their construction, the specifications re- 
quired by the Bureau of Construction and Eepair are quoted : 

1. Motors to be wound for 120 volts, direct current, for both arma- 
ture and field windings, unless otherwise specified, and to be either 
series, shunt, or compound wound, according to work they are to per- 
form. 

2. In sizes above 4 horsepower, motors to be multipolar; 4 horse- 
power or below may be bipolar. Motors are to be as compact and light 
as possible, consistent with strength and efficiency. The method of 
running wires to motors to be in all cases by tapping conduit directly 
into the motor frames or into connection boxes attached to frames, as 
may be specified in each individual case; connection boxes for inclosed 
motors to be water-tight. 

Inclosed motors should be provided with openings of sufficient size 
and number to give easy access to brush rigging, commutator, and 
field coils; such openings to be provided with covers and fastenings of 
approved design. The contact surfaces between these covers and motor 
frame should be flat machined surfaces, provided with rubber gaskets. 
Eubber gaskets for all water-tight work to be in accordance with the 
Navy standard specifications for the same as issued by the Bureau of 
Supplies and Accounts. All inclosed motors to be provided with drain 
plugs or cocks which will thoroughly drain out any water that may 
enter the motor casing. 

3. The armature shaft to be of steel and strong enough to resist 
appreciable bending under any condition of overload, to have sufficient 
bearing surface, and to be efficiently lubricated by grease or self-oiling 



292 Naval Electricians 7 Text Book 

bearings, as occasion may require. Bearings are to be provided with 
bronze or split babbitted bearing linings. Oil rings are to be turned 
true and free from all defects; split oil rings are not to be used. A 
satisfactory arrangement to be made to prevent oil from running along 
the shaft or being spilled. Visual oil gauges to be provided for deter- 
mining the amount of oil in pocket and drains for drawing oil prior to 
renewal, and in addition an overflow outlet attached directly to the 
bearing, at such a height that it will prevent oil entering the motor 
frame to be supplied. 

4. A name plate bearing the following data is to be attached to the 
motor frame: Name of manufacturer; shop number; type and class; 
date of manufacture; the winding, voltage, amperes, horsepower out- 
put, and revolutions per minute at rated load; the Bureau by which 
ordered, requisition number, and date of acceptance; also space to be 
provided for stamping the name of the vessel on which the motor is 
used. 

Armatures and Field Coils. 

5. All the field poles to be equally energized. In compound motors, 
series and shunt windings to be separate and so arranged that either 
winding may be removed without disturbing the other. The windings 
of armature and field to be well protected from mechanical injury and 
to be painted with water-excluding material not soluble in oil or grease. 
No insulating substances to be used that can be injured by a tempera- 
ture of 100° C. 

The armature to be of the ironclad type, built up of thin laminated 
disks of soft iron or steel of the very best quality, having the spaces 
between the teeth punched out of each separate disk and not milled 
after assembly. 

The disks to be properly insulated from each other. The coils to be 
preferably of the removable type and to be retained in slots of the 
armature body by maple wedges running full length of armature, or* 
other approved method. Band wires must be of nonmagnetic material 
in wake of pole pieces. The armature to be electrically and mechanic- 
ally balanced. The windings at pulley end to be protected from oil in 
an approved manner. The commutator segments to be of pure hard- 
drawn copper. The segments to be of ample depth and insulated from 
each other and the shell by pure mica of such quality as to secure even 
wear with the copper. 

Brush Rigging. 

6. Brushes to be of carbon; current density in brushes must always 
be given and should be in accordance with the best practice. Special 
attention must be given to the selection of brushes, that their material 
may be homogeneous and the quality such as to give perfect commuta- 
tion without cutting, scratching, or smearing the commutator. Brush 



Service Motors 



293 



holders to be readily accessible for adjustment and renewal of brushes 
and springs; to be entirely of noncorrosive metal and of the sliding 
shunt-socket type, in which the brush slides in the holder and is pro- 
vided with a flexible connection between brush and holder. The springs 
are to be phosphor-bronze and shall not be depended on to carry current. 
Brush holders on all motors to be adjustable for tension, and on motors 
of 5 horsepower and above to be adjustable for tension without tools, 
and so constructed as to permit of proper staggering of brushes. Brush 
holders for nonreversible motors of 5 horsepower and above to be sim- 
ultaneously adjustable for position. Proper position of rocker arm to 
be plainly marked. This position for reversible motors to give same 
speed in either direction. 




Fig. 117.— CB-15 Motor. Gen. Elec. Co. 



Types of Motors. 

Several types of motors are shown in the following cuts and have 
been chosen to illustrate typical forms and a knowledge of their 
construction and of the various parts that go to make a completed 
machine may be gained by a study of the figures showing the 
exploded views. 



Si 111 







^ ^R P^ > r 
^ 0$ U £ ,0"£ 







Service Motors 295 

The motors are made by the General Electric Company to con- 
form to specifications, either present or past. 

Figs. 117 and 118 show respectively an assembled view and an 




Fig. 119.— CB-25 Motor. Gen. Elec. Co. 

exploded view of motor known as CB-15, nsed in some instances for 
12-inch elevating motors and whip-hoist motors. 

Figs. 119 and 120 show an assembled view and an exploded of 
motor CB-25, a series motor, nsed principally for boat cranes. 

A longitudinal section of a CB-25 motor is shown in Fig. 121. 



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Service Motors 



297 




298 Naval Electricians' Text Book 

Electrical Construction. 

The winding of the armature and fields of motors is determined 
by the voltage to be impressed on the motor terminals, and different 
classes and types of motors vary in the style of winding adopted, 
in the number and arrangement of poles and in the number, wind- 
ing, and size of conductors. As examples of the electrical con- 
struction of different types of motors used in ship installation, a 
description is given of motors used for chain ammunition hoists, 
turret turning, and boat-crane revolving. 

Chain Ammunition-Hoist Motor. 

Motor. — This is shunt wound, designed for 400 revolutions per 
minute at 125 volts. 

Magnet Frame. — The magnet frame consists of a cast-steel shell 
separable in a horizontal plane through the axis, with bored seats 
for the pole pieces and feet for fastening the motor to its support. 
Hand holes are furnished with suitable covers to give access to 
the commutator and brushes. 

Pole Pieces. — There are four pole pieces, two cast with the upper 
and two with the lower half of the magnet frame, and are provided 
with laminated steel pole tips secured in place by bolts passing 
through the pole pieces with nuts on the outside of the magnet 
frame in cored pockets. 

Armature Bearings. — The armature bearings are carried in bored 
seats in the ends of the magnet frame which fit accurately, thus 
insuring perfect alignment at all times. Each is held in position 
by four hexagonal head cap screws, two in each half of the frame. 
The bearing at the commutator end contains the cone brake. 

Each bearing is of the self-oiling type, carrying a large oil reser- 
voir below the shaft, one oil ring furnishing ample lubrication. 
Each bearing is provided with a slot in the top which allows the 
insertion and inspection of the oil rings and rilling the oil well. 
Sight oil gauges are cast with the bearings and means are provided 
for drawing the oil from the reservoir. 

Linings. — These are of bronze in one piece, fitting accurately 
bored seats in the bearing and held from turning by set screws. 



Service Motors 299 

Field Coils. — The four field coils, each fitting around and held 
in place by its pole piece, are insulated with varnished cambric 
and tape, and then treated with several coats of insulating baking 
japan to give them a high insulating quality and at the same time 
to make them thoroughly water-proof. The ends of the windings 
are soldered to connectors. 

Armature. — The armature is of the drum-wound type. The 
core consists of soft steel laminations securely keyed to the shaft 
and held in position by cast iron end discs, the core being slotted 
to retain the armature coils. The coils are form wound and securely 
held in slots of the armature core. 

Commutator. — The commutator consists of a malleable iron shell 
supporting segments of hard drawn copper carefully insulated with 
mica. The commutator is securely keyed to the shaft. The ends 
of the armature coils are soldered into the commutator segments. 

Brush Rigging. — The brush rigging consists of specially-treated 
insulating blocks, supported from the frame and carrying two radial 
carbon brushes held against the commutator by adjustable springs. 

Cables and Connections. — The armature and field cables are 
brought through rubber gaskets at the commutator end of the 
frame, insuring accessibility and water-tightness. 

Non-Corrosive Parts. — All screws, nuts, etc., which are liable to 
become corroded and broken in removal are made of non-corrosive 
metal, not of iron or steel. Flat springs are of phosphor bronze 
and spiral springs of steel, copper plated. 

Test. — The motor should deliver 3 horsepower at the armature 
shaft when running 400 revolutions per minute at 125 volts, for 
a continuous period of two hours, the temperature of the various 
parts above the air at the end of this time should not exceed the 
following : 

Armature winding ...45° C. by thermometer. 

Field windings 50° C. " resistance. 

Commutator 50° C. " thermometer. 

Bearings 45° C. " 

The motor should stand an overload of 50 per cent for five min- 
utes without injury. 

All windings should withstand a high potential test of 1500 volts 
alternating for one minute. 



300 



Naval Electricians 7 Text Book 



Efficiencies. The efficiency of this motor at the armature shaft 
should be as follows : 

% load 60.5 per cent. 

% " ....74.5 " " 

% " 77.5 " " 

Full load 79.0 " " 




Fig. 122.— CB-27 Form B Motor. Gen. Elec. Co. 



Brake. — There is an electric cone brake forming a part of the 
commutator end bearing. This is so arranged that the braking 
friction is released when the operating coil is excited and set when 
the current fails. This coil is entirely protected from mechanical 
injury and is so designed that it can be replaced in case of damage. 

Panel. — The motor is controlled by the type known as U. S. 
Panel. 

Eig. 122 shows an assembled view of motor known as CB-27, 
used on chain ammunition hoists, while Fig. 123 shows a longi- 
tudinal section of the same motor. 



Service Motors 



301 



A Turret-Turning Motor. 

Classification. — This motor is of the armored type, shunt wound, 
and classified as CB-24-A2-35 H. P.-354 E. P. M.-80 Y. 

Note. — The first three figures and letters indicate the manufacturers 
shop number; type and class. 35 H. P. means that at its rated speed 
the output of the motor is 35 horsepower; 354 R. P. M. means that at 
its rated load, the armature shaft will make 354 revolutions per 
minute; 80 V means that the E. M. F. to be impressed on the terminals 
to produce the rated horsepower and speed is 80 volts. 




Fig. 123.— Assembly of CB-27 Motor with EC-104 Brake. 



Magnet Frame. — The frame is cast steel, octagonal in shape, and 
separable in a horizontal plane to allow of easy access to the arma- 
ture and field windings. The frame is entirely enclosed, this being 



302 Naval Electricians' Text Book 

a characteristic of the armored type, but access to the brushes, com- 
mutator, and connections is afforded by four oval-shaped openings 
at each end of the frame and three rectangular-shaped openings 
in the upper frame at the commutator end. These openings are 
provided with water-tight covers held in place by clamping bolts. 

Pole Pieces. — The pole pieces are four in number, made of cast 
steel, held in place by one bolt and so shaped as to securely hold 
the field coils. 

Field Coils. — The field coils, four in number, fit around and are 
held in place by the pole pieces. Each coil consists of 1080 turns 
of .102-inch diameter, No. 10 B. & S. double cotton-covered wire. 
The coils are form wound, thoroughly insulated with varnished 
cambric and tape and treated with insulating baking japan. Suit- 
able terminals are provided on the coils for the electrical connec- 
tions which are arranged for separate excitation. 

Armature. — The armature is of the drum-wound type, multiple 
connected. The core is made up of steel laminations, mounted on 
a cast-iron spider keyed to the armature shaft, having suitable slots 
for the armature coils and air ducts for ventilation. 

The armature coils are form wound, thoroughly insulated with 
varnished cambric and tape, and made water-proof with japan. 
Each coil consists of two copper bars .07" X -42" in multiple. 
There are 66 slots and 132 single coils, making four conductors per 
slot. The slots are thoroughly insulated and the coils held in place 
by bands of phosphor bronze wire. 

Connection between the armature coils and the commutator bars 
is made by copper clips, the joints being soldered. 

Commutator. — The commutator is of the ventilated type and con- 
sists of hard drawn copper segments 132 in number. These are 
mounted on a cast-iron spider and held in position by two cast- 
steel cone rings. Mica insulation is used throughout. 

Brush Rigging. — The brush rigging consists of four insulated 
studs carried on an adjustable yoke. Each stud carries four brush 
holders with adjustable tension springs and each brush holder 
carries one carbon brush 1-J" X 1" provided with flexible cables or 
pig-tails. Alternate brush studs are connected by bus rings. 



Service Motors 303 

Cables. — All cables are treated with water-proof compound, and 
brought through the frame through standard stuffing tubes. The 
field cables are 100 No. 25 B. & S. extra flexible brush-holder cables 
■J inch in diameter over all. The brush cables are 1000 Xo. 25 
B. & S. extra flexible brush-holder cable 1.16 inch in diameter 
over all. 




Fig. 124.— CB-32 Motor. Gen. Elec. Co. 

Figs. 124 and 125 show the assembled and exploded view of 
motor known as CB-32. 

Boat Crane Revolving Motor. 

Classification. — This motor is series wound, of the armored type, 
and classified as GE-800-E, 20 H. P., 310 R. P. M., 80 volts. 
Magnet Frame. — The frame is cast steel, rectangular in shape, 



Service Motors 305 

and cast in two parts to allow of free access to the armature and 
field windings. The lower half has suitable feet for fastening the 
motor to its foundation. The frame is entirely enclosed, but a 
suitable hand-hole provided with water-tight hinged cover allows 
for inspection and adjustment of the brushes. 

Pole Pieces. — There are two salient and two consequent poles 
cast with the frame. 




Fig. 126.— CB-25 M. 8, 30 H. P., 310 R. P. M., 125-Volt Ammunition- 
Hoist Motor with ED, 108 Disc Brake. Gen. Elec. Co. 

Bearings. — The armature bearings have the lower part cast with 
the lower frame. The upper part is a removable cap containing a 
grease box, grease lubrication being used. An opening underneath 
provides for the escape of the grease after it is used. The bearing 
linings are of cast iron, babbitted, made in halves. 

Field Coils. — The field coils are two in number fitting around 
the salient poles and held in position by bolts and clamping frame. 
Each coil consists of 33 turns of two .289-inch diameter copper 
wires, Xo. 1 B. & S., in parallel. They are asbestos and single 
cotton covered and the ends of the windings are soldered to suitable 



306 



Naval Electricians' Text Book 



terminals for making the electrical connections. The coil is then 
thoroughly insulated with varnished cambric and tape, and made 
water-proof with insulating baking japan. 

Armature. — The armature is of the drum-wound type, series con- 
nected. The core is made up of steel laminations mounted on the 
shaft and firmly held between the armature heads. Suitable slots 
are provided for the armature coils and air ducts for ventilation. 

The armature coils are form wound, thoroughly insulated with 
varnished cambric and tape, made water-proof with japan, and held 
in place by bands of phosphor-bronze wire. Each coil consists of 



m 




•Be, a,-£ 




/ s^^>>*» , * 






Fig. 127.— CB-34 Motor. Exploded View. 



A = Magnet Frame, Lower Half. Ra ■ 

B = Magnet Frame, Upper Half. S = 

C = Bearing Head, Commutator End, Upper T ■■ 

Half. 77- 

D = Bearing Head, Commutator End, Lower V ■■ 

Half. Va ■- 

E = Bearing Head, Pinion End, Upper Half. W ■■ 

F = Bearing Head, Pinion End, Lower Half. X = 

G = Bearing Lining, Commutator End. Y ■ 

H = Bearing Lining, Pinion End. Z 

I = Pinion Rey. Za - 

J = Armature. Aa ■ 

K = Commutator. Ba - 

L = Oil Ring, Commutator End. Ca ■ 

M = Oil Bing, Pinion End. Ba -. 

iV = Leather Oil Washer, Commutator End. Ea - 

O = Leather Oil Washer, Pinion End. Fa ■- 

P = Brass Retaining Ring for Oil Washer, Com- Ga ■ 

mutator End. Ha ■ 

Q = Brass Retaining Ring for Oil Washer, Pin- la ■ 

ion End. Ja - 

Qa = Field Coil. Ka -- 

B = Brass End-Plate Commutator Bearing. La - 



Field Coil Terminal. 

Spool Flange. 
: Pole Piece. 

Pole Piece Bolts. 

Rectangular Hand-Hole Covers. 

Rubber Gasket for Hand-Hole Covers. 

Round Hand-Hole Covers. 

Wrench Bolts for Hand-Hole Covers. 

Bolts for Bearing Heads. 
i Bolts for Magnet Frame. 

Bolts for Bearing Heads and Magnet Frame. 

Brush-Holder Yoke. 

Brush-Holder Lug and Cable Terminals. 

Brush-Holder Bus Cables. 

Field Cables. 

Brush-Holder Cables. 

Oil Gauge Commutator End. 

Carbon Brush. 

Brush-Holder Spring. 

Brush Holder Complete. 

Brush-Holder Stud. 

Insulation Washers for B.-H. Stud. 

Insulation Bushing for B.-H. Stud. 



308 Naval Electricians' Text Book 

one turn of four No. 10 B. & S. .1018-inch diameter copper wire 
in multiple, with extra heavy double cotton-covered insulation. 
There are 105 slots and 105 coils making two conductors per slot. 
The ends of the coils are soldered into the commutator bars. 

Commutator. — The commutator is of the ventilated type and con- 
sits of 105 hard drawn copper segments on a malleable-iron spider 
and held in place by two malleable-iron cone rings. Mica insula- 
tion is used throughout. 

Brush Rigging. — The brush rigging consists of four insulated 
brass studs mounted on an adjustable yoke. Each brush holder 
contains one brush 2£" X f" provided with a flexible cable or 
pig-tail. 

Cables.— All cables are 300 No. 25 B. & S. extra flexible brush- 
holder cable, ||- inch outside diameter. They are treated with 
water-proof compound and brought out of the frame through drilled 
and tapped holes to which conduit may be attached. 

Ammunition-Hoist Motor. 

Fig. 126 shows an assembled ammunition-hoist motor fitted with 
electric brake. 

Fig. 127 shows an exploded view of motor CB-34. 

Fig. 128 shows a longitudinal section of CE motor, form G> and 
is of particular interest in showing all the different materials used 
in the construction as shown in the key to sectioning. 

Blower Motors. 

A design of motor for use with ventilating fans and blowers 
which finds extensive use on shipboard is shown in Fig. 129. It 
is made by the B. F. Sturtevant Company and is used with fans 
and blowers made by the same firm. 

Description of Motors. — A motor, classified as M. P.-8 fan 
motor, is of the 8-pole type, and is especially designed to be direct 
connected to the side of the steel plate blowers of the centrifugal 
type. It is supported from the side of the blower by a cast-iron 
plate, which has three lugs for securing to the field frame or magnet 
ring of the motor. This cast-iron plate forms a part of the side 



Service Motors 309 

of the blower and is secured to the same by means of through bolts, 
which are easily removable. 

Motor Parts — Magnet Frame. — The magnet frame or field ring 
consists either of a cast-iron ring, which is machined on the two 
faces and bored out on the internal surface to receive the pole 




Fig. 129. — Sturtevant Eight-Pole Motor. Arranged for Attachment to 
Side Plates of Fan. 

pieces, or of a wrought iron or steel casting which is machined all 
over both inside and out. The magnet ring is indicated on Fig. 130 
by (1), and to the inner machined surface of which are secured 
by the bolts (27), the pole pieces (4). 

Pole Pieces. — These pole pieces usually consist of Norway iron 
field cores with cast-iron shoes attached, but some are made of a 
solid steel casting. 



310 Naval Electricians' Text Book 

Field Coils. — The pole pieces (4) are each encircled by the field 
coil (6), which consists of double cotton-covered magnet wire of 
highest conductivity, machine wound upon a form, after which it is 
thoroughly insulated by the following process : 

1. Baked two hours at 150° F. to exclude all moisture. 

2. Given two layers of heavy cotton tape. 

3. Saturated with an insulating compound of highest possible 
moisture resisting qualities. 

4. Baked five hours at 150° F. 

5. Given two layers oiled rope tape. 

6. Given two layers of finishing tape. 

7. Finished with a heavy coat of quick-drying, black, oil, water 
and acid-proof insulating varnish. 

After this treatment, and being placed on the pole pieces, a 
break-down test of 2500 volts is applied for one minute. These 
field coils are supplied with flexible leads, which are connected as 
hereinafter described. 

The field coils of all these motors are made of double cotton- 
covered magnet wire. 

Armature. — The armature (5) consists of a core (3) of lami- 
nated punchings of low steel clamped between two cast-iron flanges 
(25 and 26) the whole being wound upon a cast-iron spider (2) 
and the whole being held firmly in place by the screws (32). The 
laminated punchings are of No. 26 gauge, and have their slots for 
receiving the armature coils punched by the " step-by-step " process 
upon an indexing press. On account of the large diameter and 
open construction of this armature, together with the extremely 
narrow construction of the core ventilating discs through the core 
are not necessary, perfect ventilation being attained by the freedom 
with which the air may circulate through and about the entire 
armature. 

The armature is of the form-wound, coil-drum type, having all 
coils duplicates and machine wound. Before being placed upon the 
core all coils are thoroughly insulated, additional insulation being 
placed in the slots as an extra precaution. This insulation con- 
sits of horn fibre or laminated rag board of varying thickness ac- 
cording to the work. For armatures of the size used on the 4-100 



Service Motors 311 

type M. P.-8 motors, the following method of excluding moisture 
and providing additional insulation is used: After the armature 
is completely assembled it is baked for from three to four hours at 
150° F. to drive off all moisture, after which they are immediately 
thoroughly saturated with the Standard Varnish Works' Extra 
Black Coil Varnish. The armature is then again baked for about 
twelve hours at from 150° to 175° F. They are then allowed to 
cool slightly, after which they are finished with the Standard 
Varnish Works' Black Finishing Varnish. This process is the same 
for all armatures, except for the length of time required to bake 
them, which is less for smaller and more for larger motors. 

Commutator. — The commutator (36) consists of pure drop- 
forged or drawn copper segments (7) clamped in a shell (17) by 
means of the screws (16.) and thoroughly insulated by the micanite 
rings (37). Pure amber mica only is used between the segments. 

This commutator when completed is mounted directly upon a 
projection from the armature spider, being held in place by a key 
(24) or four flat-head screws. The entire assembled armature is 
then forced upon the shaft of crucible steel (11), to which it is 
firmly secured by the key (10), upon the top of which is a set screw. 

Bearings. — The bearings are of the ring-oiling type and consist 
of two composition sleeves (8 and 22), the rear bearing being of 
self -aligning construction and having two oil rings (33), while the 
front sleeve (22) has only one ring (13). The front sleeve (22) 
is held in place by two screw pins (14), and the back sleeve is 
held in the box (9) by screw pins, which are not shown upon the 
plate. The front bearing sleeve is supported in a tripod hanger or 
3-armed yoke (23), which yoke is firmly secured to the magnet 
ring (1) by the six cap screws (31). Eemoving these cap screws 
allows this tripod hanger to be removed from the machine, after 
which the armature may be readily withdrawn from the field. 
Before doing this, however, the brush rigging must be removed 
from its supporting brackets (29). The back-bearing sleeve (8), 
as above stated, is supported in a cast-iron box or shell (9), which 
is secured to the cast-iron fan bracket of plate (28) by cap screws 
(15). This cast-iron fan bracket (28) supports the entire motor 
by being secured to the field frame by the cap screws (34), and 




1 

ft 
B 

o 
O 



Service Motors 313 

the entire machine is secured to the side of the fan by through bolts 
which pass through the holes (35). 

Brush Rigging. — The brush rigging is of special construction and 
consists, first, of a guide ring (12), which is supported in the 
brackets (29), to which guide ring are secured by the through bolts 
(18), the two stud rings (19), to which are riveted the brush- 
holder studs (21). This brush rigging is so designed that all the 
studs of like polarity are attached directly to one stud ring, and 
all studs of opposite polarity are attached directly to the other. 
These two stud rings (19) are thoroughly insulated from each other 
and from the guide ring (12) by the hard rubber insulating washers 
and bushings (20). By loosening the small screws (38) this entire 
brush rigging is free to revolve around its axis. 



CHAPTER XVII. 

MOTOR STARTING AND CONTROLLING DEVICES. 

Rheostats. 

A rheostat is an arrangement of conductors for reducing the 
amount of electrical current passing through any circuit by inter- 
posing a resistance in it. A certain amount of the potential of the 
circuit is used up in overcoming the resistance of the rheostat and 
this represents the energy dissipated as heat. Eheostats should be 
used as little as possible, though in many cases, like shunt field 
regulators of generators they must be left in the circuit con- 
tinuously. 

In general, a rheostat consists of an electrical conductor properly 
supported, insulated, and provided with binding posts for making 
connection to the main line and to the apparatus to be controlled. 
The conducting materials generally used are German silver, nickel- 
ine or iron. Rheostats for regulating shunt field of dynamos 
ought to be made of German silver or some such alloy whose re- 
sistance does not change much with rise of temperature. Iron is 
not much used for resistances on board ship, on account of its 
liability to rust. 

The conductor must be properly supported and well insulated 
from its supporting frame and must be so mechanically built as to 
allow effective ventilation, as the heat produced by the electrical 
currents must be carried away by radiation and convection. 

Rheostats that are used only intermittently will carry a much 
larger current for a short time than those which are used con- 
tinuously, as they will absorb a large amount of heat in a short 
time without becoming dangerously hot, but must be allowed to 
cool before being used again with large currents. 

General Requirements. — The material of all resistances should 
be non-corrosive and not damageable by heating to a temperature of 



Motor Starting axd Controlling Devices 



315 



150° C, or by salt air or salt water, and should not materially 
change its resistance with rise of temperature. 

The insulating material 
should be non-combustible, 
non-absorbent and not dam- 
ageable by moisture or by 
heating to a temperature of 
150° C. The resistance 
should be so supported that 
it will not fall out in case it 
should be melted off or over- 
heated at any point, and 
should be insulated from the 
supporting frame and the 
frame insulated from the 
hull of the ship. 

Packed Ribbon Rheo- 
stats. — This is the general 
form of rheostat used where 
large current capacity is re- 
quired, as in turret ammu- 
nition hoists, gun rammers, 
and elevators, boat cranes, 
deck winches, whip hoists, 
etc., and is distinguished in 
description as " PE " rheo- 
stats. 

These rheostats are built 
up in units and a character- 
istic completed one is shown 
in Fig. 132, while the de- 
tailed parts are shown in 
Fig. 131. It consists of two 
cast-iron end frames held in 
position by four round tie 
rods. Each end frame has 
a fire-brick with six slots 




316 



Naval Electricians' Text Book 



cemented to it. These fire-bricks support six panels of filling, dif- 
fering somewhat in the various rheostats, but consisting essentially 
of malleable-iron top and bottom strips, provided with binding 
posts, between which are stretched back and forth several layers 
of German silver ribbon, the different layers being insulated from 
each other by means of asbestos. In addition to the German silver 
resistance, many of the panels have iron radiating pieces inserted 
between the various layers to help dissipate the heat. These 
rheostats are generally mounted so that the panels lie in vertical 




Fig. 132. — Pressed-Ribbon ("PR") Rheostat. Gen. Elec. Co. 



planes, allowing the air to circulate freely between them and thus 
carry off the heat. In order to prevent the absorption of moisture, 
these panels are dipped in japan which makes them water-proof. 

The binding posts consist of lugs, provided with set-screws, cast 
on top and bottom plates. A binding post is provided at both ends 
of each panel for convenience in making connections. The panels 
are connected together by short copper strips fastened by screws to 
the top and bottom plates. The connections are usually made so 
that the six panels of the rheostat are in series with each other, but 
in some cases longer strips are used, so that the panels are connected 



Motor Starting axd Controlling Devices 



317 



either two or three in multiple. These rheostats are designated by 
a serial number, as P. K.-218. If the panels of the rheostat are 
connected two in multiple the series number is followed by the letter 
A, as P. K.-218-A, and if connected three in multiple, it is known 
as P. K.-218-B. 

The panels are insulated from the iron frames by means of the 
fire-bricks, but in order to give more insulation, insulating bush- 
ings are provided for the bolt holes in the feet of the rheostat 




Fig. 133. — Wound Tube and Pressed Cards. 



frame, so that each rheostat frame is insulated from its support. 

Pressed Card Rheostats. — These rheostats are used where small 
current capacity but considerable resistance is required, as in the 
field circuits for controlling the voltage of generators or the speed 
of motors and in armature circuits for starting or controlling small 
motors. Eesistances to take up field discharge on opening field 
switches are also of this type. 

They are distinguished in description as " PC " rheostats. A 
completed unit is shown in Fig. 134, and various kinds of separate 
windings in Fig. 133. 



318 



Naval Electricians' Text Book 



This rheostat uses a filling made of German silver wire, wound 
on a mandrel covered with a tube of asbestos. After winding, the 
tube surrounded by the wire is pressed into a Y-shaped trough or 
card, the turns of wire being sufficiently far apart to prevent them 
from becoming short-circuited. Several of these cards are packed 
together and held between pressure plates made made of cast iron 
thoroughly insulated with mica. The whole bunch of cards thus 
clamped together is supported by rods passing through the pressure 




Pig. 134. — Showing Iron Plates Between Cards. 



plates which are held in place by nuts. These rods are then fast- 
ened in cast-iron brackets or legs, to which the slate carrying the 
contact blocks of the rheostat is also attached. After the cards 
have been assembled, they are thoroughly treated with japan to 
make them water-proof. 

Enclosed Card Rheostats. — These rheostats are for the same gen- 
eral purposes as the pressed card type and are somewhat similar in 
construction. They are designated as "EC " rheostats. 

The rheostat frames are made up of two perforated cast-iron end 
pieces and two perforated sheet-iron side plates. The resistance 



Motor Starting and Controlling Devices 319 

units are mounted within the frame. The illustration in Fig. 135 
shows an enclosed card unit in its four stages of construction. 

Each resistance unit consists of an asbestos tube around which 
the resistance wire or ribbon is wound. The tube is then pressed 
flat and enclosed in an asbestos-lined japanned sheet-metal casing. 
These units are assembled on mica insulated supporting rods and 
are spaced and insulated from one another by mica washers. 




Fig. 135.—" EC " Rheostat Elements. 

Resistances are secured by using two or more units, in series, and 
higher carrying capacities are obtained by connecting plates in 
parallel. 

The button terminals are shown in the diagram of connections 
in Fig. 136. 

The switches of these rheostats have three rows of contact buttons. 
The short arm of the switch is attached to the hand-wheel, through 
the shaft, and bears upon the inner row of contact buttons. The 
long arm revolves freely about the shaft and is insulated from the 
short arm. Upon the long arm is a contact brush connecting the 
outer and intermediate rows of contact. The intermediate and 
inner rows or dials are tied together. When both arms are in line, 
one over the other, on the first buttons of the dials, the resistance is 
all short-circuited. The desired amount of resistance can be cut 
in by turning the handle to the right. When the short arm has 
made half a revolution a projection on it strikes a pin in the long 
arm and carries it along, inserting the resistance connected to the 



320 



Naval Electricians' Text Book 



outer dial. The reverse movement causes the short arm to strike 
the long arm direct, after making half a revolution and carries it 
back. 

The rheostat is so arranged that one-half revolution of the short, 
or inner, contact arm cuts in or out a resistance equal to that in 
one step of the outer dial thus permitting fine regulation. 

" CG " Rheostats.— The " CG " or cast grid rheostat, shown in 
detail in Fig. 137, consists of a number of cast-iron resistance units 




Fig. 136.— Connections of "EC" Rheostat. Gen. Elec. Co. 



of the shape shown in the photograph, mounted upon insulated 
rods, the latter being held in cast-iron end frames. 

The developed length of these grids is the same for all resist- 
ances, the difference in resistance being obtained by varying the 
cross-section of the casting. 

Bosses, through which the supporting rods pass, are cast at one 
end of these grids, these being somewhat thicker than the remain- 
ing material, so that when the grids are mounted upon the sup- 
porting rods, they are separated by an air space, the connection 



Motor Starting axd Controlling Devices 



321 



between the various grids being made at the above-mentioned 
bosses. 

Mica washers are inserted between these bosses where it is de- 
sired to separate the grids, and provision is made for connecting 
leads by means of cast-iron terminals, which are inserted between 
the bosses above described. 

This type of rheostat possesses a great advantage of having large 
intermittent capacity, since the resistance material can be heated if 
necessary to very high temperature, and the heat thus generated is 




Fig. 137.— " CG " Rheostat. Disassembled View. Gen. Elec. Co. 



rapidly dissipated by the large radiating surface of the grids. This 
design of rheostat permits wide range of resistance capacity deter- 
mined by the size of grid and the use and arrangement of these 
grids in series or multiple. 

" IG- " Resistance. — The form " IG- " resistance, shown in the 
upper part of Fig. 138, is similar to the form " CG " rheostat above 
described, the principal difference consisting in the shape and 
dimensions of the grids. 

They are used ordinarily for motor starting resistance, in series 
with the armature circuit. 



222 



Naval Electricians' Text Book 



" ES " Resistances. — The " ES " or edgewise wound resistance 
unit, shown in Eig. 139, consists of a resistance ribbon, rectangular 




Fig. 138.— Type UY, Form K, 60 H. P. Combined Starter and 
Regulator Panel. Gen. Elec. Co. 



in section, wound on edge around a supporting tube, from which it 
is insulated ordinarily by asbestos. 



Motor Starting axd Controlling Devices 323 

After the spiral has been wound, the turns are separated and the 
entire unit dipped in a silicate, which, when hardened, separates 
the whorls and covers the outside of the resistance, making it solid 
and able to withstand a very high temperature. 

Form " P " Resistance. — The form " P " resistance, shown in 
Fig. 140, consists of an asbestos tube supported at the ends by 
porcelain bushings, upon which the resistance material is wound, 
the whole tube being coated by a silicate after it is completed. 

This unit will stand a very high temperature without injury and 
has a large radiating capacity. It is made in several standard sizes, 
and in special cases, taps are brought out to meet requirements, 
although ordinarily there are but two taps, one at each end. 




<f 






o o 



Fig. 139. — Edgewise Wound Resistance Coil. Gen. Elec. Co. 

Rheostats for Controlling Panels. — Rheostats for the controlling 
panels of ventilating motors of the Cutler-Hammer make are known 
as the " sand box " type. The resistance is wound on a thin slate 
slab located in the center of an iron box and surrounded by glass- 
makers' sand. There is a filling hole plugged by a pipe plug. The 
front of the box is of cast iron for the small rheostats and slate 
for the large ones. 

The contact buttons are located on the front of the box, insula- 
tion with mica in the case of the small rheostats with metal fronts. 
Wire connectors connect these contacts with the switch contacts on 
the front of the panel. The rheostat is insulated from the panel 
framework by hard rubber bushing. 

Other forms of rheostats are made with the resistances coiled on 



324 



Naval Electricians' Text Book 



porcelain tubes or embedded in enamel. In the latter form the 
resistance is generally in the form of corrugated ribbon to allow it 
to be coiled in a small space and to present greater radiating sur- 
face for the heat produced. 

Liquid Resistances. — Although these find no use on shipboard 
they are useful in the laboratory to provide non-inductive loads 
when testing generators. They generally consist of iron plates im- 
mersed in water, or salt or soda solutions, and the resistance may 
be regulated either by moving the plates nearer together or farther 




Fig. 140. — Type FM, Form " P ", Field Rheostat. Gen. Blec. Co. 



apart from each other, or by immersing a smaller or larger area of 
plate, effected by having wedge-shaped plates. 

The chief troubles with these resistances are the evaporation of 
the water and the creeping of the dissolved salts. The creeping 
can be avoided by smearing vaseline just above the liquid level. 

Starting and Controlling Devices. 

These are devices installed between the power supply mains and 
motors for starting or stopping them, reversing the direction of the 
armature or for changing their speed. 



Motor Starting and Controlling Devices 



32; 



The} 7 are used where particularly heavy currents are not required, 
as in chain ammunition hoists, hull ventilating motors, all separate 
ventilating or smoke-blower motors, in separate machine motors, 
and all auxiliary motors used for independent purposes, as laundry 
work, meat choppers, ice-cream freezers, potato peelers, printing 
presses, etc. 

Principles of Automatic Rheostats. — There are several varieties 
of these devices. One form used for motor starting has a magnetic 







Fig. 141. — Starting Resistance. 



device to throw the starting resistance into series with the armature 
in case the line voltage is removed for any cause. Others have, in 
addition, a device to throw the starting resistance into the armature 
circuit and thus slow or stop the motor in case of a dangerous 
overload. Others have starting devices in which the resistance is 
cut out automatically. 

Fig. 141 illustrates a form of rheostat combining the principles 
to be satisfied for starting rheostats for all shunt motors. 



326 Naval Electricians' Text Book 

The starting resistance in series with the armature M is shown 
marked 8R and its necessity has been explained under Operation of 
Motors. The shunt field connection runs from D on the + side 
of the supply mains to B through the magnet R, thence through the 
motor field F to the — main. It will thus be seen that the field is 
fully energized when the switch in the main line is closed, and this 
is an important principle in all starting panels or rheostats. If by 
any chance there was only a weak field on starting, it would result 
in an excess of current and heavy sparking. 

When the main switch is closed and the field excited, a movement 
of the rheostat arm to the right making contact on point No. 1 
connects the main line to the armature through the starting resist- 
ance on the left, through the arm, through the starting resistance 
on the right, around the magnet 0, through terminal C to arma- 
ture M and to the — line. 

The operation of starting the motor is, after contact is made on 
contact 1, to slowly move the arm over the successive contact points, 
cutting out resistance, until it rests on the last contact, when all 
resistance is out and the arm brings up against the armature of the 
magnet R. Owing to the field current flowing around R, its arma- 
ture is made strongly magnetic, holding the arm of the rheostat 
firmly by its attraction against the action of a spring tending to 
return it to its original position. 

If by any chance R becomes demagnetized by the field current 
failing, its armature will no longer attract the arm and the spring 
will throw it back to the " off " position breaking the armature cir- 
cuit and stopping the motor. As this happens when the current or 
E. M. F. fails, R is called the no-voltage release magnet. 

The main current flows around the magnet 0, and if the current 
rises above a certain amount, the magnet will attract the tripper 
arm T, which will close the circuit between two points shown which 
are connected to the terminals of the magnet R. This will short 
circuit this magnet, and as it then has no voltage, it will release the 
starting arm which will fly back to the "off" position. This 
serves the double purpose of opening the circuit due to an over- 
load and resetting the arm, so it is in the right place for restarting. 
It also serves the purpose of short-circuiting R if the starting arm 



Motor Starting and Controlling Devices 327 

is moved too rapidly and allowing too much current through the 
armature before it develops its speed. In this case, the arm will 
not be held against R when it is released by the hand but will fly 
immediately back to its starting position. For the reasons stated, 
R is called the overload magnet. 

The starting resistance of this type of controller is only made 
to withstand the current necessary to start the armature, so under 
no circumstances should any attempt be made to control the speed 
by securing the arm on any intermediate contact. 

In some forms, the overload magnet is omitted and its place 
taken by fuses in each side of the main line, and in others, both 
the overload magnet and fuses are used. 

To stop, always open the main line switch first, and the starting 
arm will fly to " off " when the field current has died down. 

Navy Standard Controlling Panel — Type TJ. S. (made by the 
General Electric Company, Schenectady, N. Y.). — The following 
applies to a standard controlling panel designed for use with motors 
supplied to the government. 

Classification. — The general design of panel is classified Type 
U. S., Form A, Form B, etc., the form letter depending upon the 
electrical connections which are different according to the kind of 
apparatus to be operated and to the method of operation. 

Construction. — The dimensions and general design of this panel 
for motors of 10 horsepower and less are shown in Fig. 142. 

Panels for motors larger than 10 horsepower are of similar de- 
sign and operation but of increased dimensions. 

The panel for 10 horsepower and less consists of an enameled 
slate 12" wide X 24" long X 1" thick, which is supported on iron 
side frames. When used on shipboard this can be enclosed by sheet- 
iron doors opening to give convenient access to the front of the 
panel. 

The enclosing casing is carefully japanned to prevent rust, the 
doors being supplied with a Yale and Towne padlock, furnished 
with duplicate keys. 

The operating parts are on the front of the slate, and the resist- 
ance is. behind the slate and supported by the side frames. 

The operating parts, common to all panels, are as follows : 



328 



Naval Electricians' Text Book 



Switch. — The main switch is at the bottom of the board. It is 
single-pole and in case of reversible motors is double-throw, inter- 
locking with a double-pole double-throw switch so arranged that 
the field cannot be opened while current is on the armature. 




Fig. 142. — Navy Standard Controlling Panel — Type U. S. Gen. Elec. Co. 



Rheostat Switch. — The rheostat switch consists of an arm carry- 
ing several contact brushes which bear upon contact rings or 
rheostat blocks, as shown in the Diagram of Connections, Fig. 143. 

This arm 3 when thrown to the extreme right, closes a single-pole 



Motor Starting and Controlling Devices 



329 






circuit breaker at the top of the panel. This is held closed by a 
retaining magnet at the upper left-hand corner, the circuit of 
which is closed by pressing down a push button near the hand of 



£)To Safety Switch Q » 




a | , — 



Armature 



O 



Looking at the Front 

Fig. 143. — Connections of Controlling Panel for Chain Ammunition- 
Hoist Motor — Type U. S. Form A. Gen. Elec. Co. 

the operator. The contact ring is so designed that this plunger 
will open this circuit and trip the circuit breaker if the hand is 
removed before the rheostat arm is on a running contact. 



330 Naval Electricians' Text Book 

Circuit Breaker. — The single-pole magnetic circuit breaker at 
the top of the board is set by the action of the rheostat arm and 
is held closed by two latches, one of which can be released by the 
overload coil when the current exceeds that for which the breaker 
is set, and the other released by the no-voltage coil. This circuit 
breaker is opened by two helical springs one released by each latch. 

The wearing parts of the circuit breaker are renewable and can 
be easily inspected by taking off the four bolts or nuts at the corners 
of the pole pieces. When the pole piece has been taken off, all 
parts of the breaker can be readily removed from the slate without 
the use of special tools. 

Fuses. — Two enclosed fuses are supplied to protect the panel 
against short circuits. 

Terminals. — The terminals consist of blocks behind the slate to 
which the wires are attached and which are held in position by 
screws projecting through the slate thus allowing connections to 
be easily made after the panel is installed. 

Resistances. — The resistances behind the slate are designed to 
meet the special requirements of the individual panel. 

Insulation. — The switch parts are mounted on a slate base which 
has been thoroughly baked and treated with japan and polished. 
Adjacent parts of the apparatus will stand a test of 1000 volts 
alternating for one minute. 

The feet of the frame are supplied with insulating bushings if 
required, which will stand 1500 volts alternating. 

Non-Corrosive Parts. — When furnished for use on shipboard, all 
small parts not in magnetic circuit are of non-corrosive material, 
and where necessary moving steel parts are copper plated. 

Weight. — The weight of the panel is approximately one hundred 
(100) pounds, slight variation being occasioned by difference in 
resistances required for various kinds of work. 

Description of Operation. — This panel is designed to protect the 
apparatus against the following conditions : 

(1) Legitimate overload. 

(2) Failure of voltage on line. 

(3) Excessive rush of current occasioned by too rapid starting. 

(4) Eunning on resistance which is only designed for starting. 



Motor Starting and Controlling Devices 331 

These features are accomplished by the fact that the circuit- 
breaker arm, which is released either by overload or no voltage 
can only be set by the rheostat arm when it is at the starting 
position and will not remain closed while the arm is on starting 
resistance blocks if the hand of the operator is removed and the 
contact at the retaining segment broken. If this occurs the no- 
voltage coil circuit is opened and the circuit breaker released. 

If the panel is used with a reversible motor, the main switch 
interlocks with the double-pole double-throw field reversing switch 
so that it is impossible to close the main line until after the field 
circuit is closed, or to open the field before the main line is opened. 

Directions for Operation. — 
To start: 

1. Close the main switch at the bottom of the board. 

2. Move the rheostat arm as far as possible to the right, setting 
the circuit breaker. 

3. Press down on push button and move the arm slowly to the 
left until the button rests in the raised surface of the contact ring. 

If the arm is moved too rapidly, or if the current fails, the cir- 
cuit breaker will open. 
To stop: 

Open the single-pole single-throw switch. 

This will release the circuit breaker which is in the side of the 
line. It is impossible to re-set this until all starting resistance 
has been placed in the circuit. 

Speed Controlling Panel. — The controlling panels previously de- 
scribed have no arrangement for controlling the speed of the arma- 
ture, but the following description illustrates this point. This 
form is used generally on ventilating fans, by which the number of 
revolutions of the fan is controlled. 

The description is of a panel of the Cutler-Hammer type and 
the connections are shown in Fig. 144. 

This type of panel is fitted with a main line switch, enclosed 
fuses, a starting rheostat with automatic no-voltage and overload 
release, and a field rheostat. It consists of an enamelled slate of 
suitable size, supported on iron side frames when enclosed; the 
back is of galvanized sheet iron and the sides and front of perfo- 



332 



Naval Electricians' Text Book 




Fig. 144.— Speed Controlling Panel. Cutler-Hamner Co. 



Motor Starting and Controlling Devices 333 

rated sheet brass. The two doors at the front of the panel are 
fastened by padlocks. The operating parts are on the front of the 
slate, and the resistances are behind the slate and supported by the 
side frames. 

Switch. — The main switch is at the top of the panel and is of the 
double-pole single-throw type. 

Rheostat Switch. — This consists of an arm carrying a single con- 
tact brush bearing on contact blocks as shown in the figure. When 
the motor is not running, the arm is held in the position shown by 
the action of a spring. 

Field Regulating Rheostat Switch. — This consists of an arm 
carrying a single contact brush bearing on contact blocks, as shown 
in the figure, and by varying the position of this arm the resistance 
of the field circuit is increased or decreased, thus increasing or 
decreasing the speed of the motor. This is only fitted for motors 
having speed control. 

Fuses. — Two enclosed fuses are supplied to protect the panel 
against short circuits. 

No-Load Release Magnet. — This magnet is placed in the field 
circuit and when the starting arm is on the " full on " position, 
this magnet retains it in position against the action of the spring 
tending to return the arm to the off position. If the line voltage 
is lost at any time, this magnet releases the arm and it is returned 
to the off position. 

Overload Release Magnet. — This magnet is in the main circuit, 
and when an excessive current passes through it, it acts upon a 
plunger which in turn acts to short circuit the " no-load " magnet, 
thus releasing the starting rheostat arm. 

Terminals. — The terminals consist of blocks behind the slate to 
which the wires are attached and which are held in position by 
screws, projecting through the slate, thus allowing connections to 
be easily made after the panel is installed. 

Resistances. — The resistances behind the slate are designed to 
meet the special requirements of the individual panel. 

Insulation. — All panels are insulated from the ship by hard rub- 
ber blocks and bushings. 



334 Naval Electricians' Text Book 

Description of Operation.— This panel is designed to protect the 
motor from the following conditions : 

(1) Legitimate overload. 

(2) Failure of voltage on line. 

(3) Running on resistance which is only designed for starting. 

These features are accomplished by the fact that the circuit- 
breaker arm, which is released by either overload or no-voltage will 
only be set and held when in the full running position by the 
no-voltage magnet. If the arm is released before it reaches this 
point, it is at once returned to the off position by the action of 
the spring mentioned above under " Eheostat Arm/' 

Directions for Operating. — To start: If the motor has speed 
control, shift the speed-control rheostat arm to the extreme position 
marked " slow " on the panel. Then close the main line switch. 
Then move the starting rheostat arm to the first contact point. 
After allowing it to remain for a moment on this point, move it to 
the second point and then to the third, etc. If the motor has not 
started when the arm reaches the fourth line segment, open the main 
line switch and ascertain what the trouble is, first making sure the 
voltage is across the mains, and then making a close examination 
into all the connections of the machine which are liable to become 
loose or displaced. As soon as the motor commences to revolve 
this starting arm should be moved slowly from one segment to the 
next until it has reached the " full on " position, at which point it 
will be firmly retained by the small magnet. After the motor has 
arrived at full speed with the starting arm at " full on," the speed 
may then be increased by slowly moving the speed-controlling arm 
from slow to fast. When necessary to reduce the speed of the 
motor, by moving the speed-controlling arm from fast to slow, this 
should be done slowly in order to allow the motor to drop in speed. 
If moved too rapidly, the motor will act as a generator, due to its 
momentum, and generate a voltage in excess of that upon the line, 
which is liable to blow the fuses, due to the excessive rush of current. 

To stop : To stop the motor, open the main line switch and allow 
the starting rheostat to take care of itself. The rheostat arm will 
not be immediately released, but will be held in place until the 






Motor Starting and Controlling Devices 



335 



on 
i 



nn- 
n 



■-] 







^-- — ot 

J©" REGULATING Q <£ 




l_ 



I 

I r— 

l , 

- F ^ OA 



M1 M2 



T7W 



Fig. 145. — Starting and Regulating Panel. Gen. Elec. Co. 



336 Naval Electricians' Text Book 

motor is slowed down somewhat, when it will fly to the " full off " 
position. 

Never attempt to stop the motor by forcing the rheostat lever to 
" full off " position ; always open the main line switch first. Be- 
fore starting again, be sure that the speed-controlling handle is at 
the " slow " point. 

Type CR, Form M-3. 

This type of starting panel for starting and field control, manu- 
factured by the General Electric Company, is shown in Fig. 145. 

From descriptions of preceding controlling panels, the action of 
this one will be readily understood. 

Separate Speed-Controller Rheostat. — These are used in connec- 
tion with a separate starting panel to control the speed of motors, 
by varying the field of the generators supplying the power, on the 
principle of the Ward-Leonard system of control previously 
explained. 

The speed-control rheostat regulates the field of the generator 
of a motor generator, the starting panel being used to control the 
current of the motor of the motor generator. 

The starting panel presents no special features, but a description 
is given of the speed-control rheostat as manufactured by the Gen- 
eral Electric Company and applied to elevating equipments for 
8, 10, and 12-inch guns. 

The general connections are shown in Fig. 146. 

The resistances are connected between contact points shown in 
the upper and lower semicircles. Each one of the upper points is 
connected to the one directly underneath it as indicated by the 
dotted lines connecting the outside ones. The ends of the generator 
field windings are connected, one to each of the two semicircular 
conductors, while one end of the supply main is connected to the 
inner circular conductor. The heavy short full lines are contact 
pieces, the right-hand one making contact between the inner and 
outer circular conductors, and the left-hand one between the outer 
semicircular conductor and the circular ring of contacts. They 
are moved by the starting arm. These contact pieces are secured on 
the outside of a toothed wheel and revolve with it, into which gears 



Motor Starting axd Controlling Devices 



337 



a toothed arc, to which the handle is secured, so when the handle is 
moved down, revolving the arc to the right, the gear wheel turns to 
the left, carrying the right-hand contact piece up and the left one 
down, as viewed in the figure. 

The direction of the current is as follows: Suppose handle is 
moved down. Current then flows from the starting panel to the 



SPEED CONTROLLING 
RHEOSTAT 




MOTOR GENERATOR SET 

Fig. 146. — Speed-Controlling Rheostat. Gen. Elec. Co. 



left-hand lower terminal, up and around to the upper right-hand 
contact in the upper semicircle, then through the resistances, 
through the left-hand contact piece to the lower semicircular con- 
ductor, then through the generator field by way of the two termi- 
nals in the right-hand lower corner, then to the upper semicircular 
conductor, from that to the inner conductor and out bv the right- 
hand lower terminal on the left and back to the starting panel. 
By moving the handle further, more resistance is cut out and 



338 Naval Electricians' Text Book 

consequently the generator field is changed, thus varying its voltage, 
which is that impressed on the working motor, and which changes 
the speed of the motor. 

By moving the handle the other way, the direction of the current 
in the generator field is changed, consequently the current through 
the generator and motor changes, reversing the direction of the 
latter. 

Automatic Motor Control. — It may happen that it is desired to 
control the arm of the motor-starting resistance automatically, so 
that the motor may be started and stopped by the simple operation 
of opening or closing a switch. Such a case arises in motor control 
in wireless telegraphy where the operator may wish to start his 
sending apparatus without leaving his station at the receiver. 

This form of control is illustrated in Fig. 147. M is the motor 
armature of the motor generator, 8 the series field, and 8' the shunt 
field with its rheostat R. 

When switch 1 is closed, circuit to the power mains is estab- 
lished through the shunt field. 2 is a single-pole switch which may 
be removed some distance from the rest of the control circuits. 
When 2 is closed, the circuit is completed through the solenoid mag- 
net 3 and the resistance 4, and when 3 is energized, its plunger is 
pulled up, and the circuit breaker 6 then completes the circuit 
through the armature M, series field 8, resistance 5, and starting 
arm 8. At the same time that the armature circuit is established, 
circuit is established in the solenoid magnet 7 and resistance 9, and 
as the magnet is energized, its plunger is drawn up, pulling up the 
starting arm 8, which gradually cuts out the resistance 5, allowing 
the motor to attain its full speed. The plunger of the solenoid 7 
works against a dash pot P, which makes its motion gradual so 
that it is not pulled up with a sudden jerk. 

To stop the motor, it is only necessary to open switch 2 when 
the magnet 3 becomes demagnetized, and the plunger no longer 
held up, drops by its own weight, opening the armature circuit, and 
at the same time opening the circuit of the solenoid 7. The 
plunger of this solenoid then drops and the starting arm returns 
to its original position throwing in all resistance in 5, and the 
whole circuit is then ready for the operation of starting again by the 
operation of closing switch 2. 



Motor Starting and Controlling Devices 



339 



When the circuit breaker 6 drops, it short-circuits the armature 
brushes through the resistance 10, bringing the armature quickly 
to rest. 




Fig. 147. — Automatic Motor Control 



Water-Tight Flame-Proof Panels. — Water-tight flame-proof 
panels are used in locations greatly exposed to moisture and where 
powder is handled as in handling-rooms, magazine passages, etc. 
Navy standard specifications require that in general they consist of 
a cast metal water-tight flame-proof case containing the necessary 
resistances, connections, and operating parts which are controlled 
from without by means of rods or levers passing through approved 
stuffing boxes. 



340 Naval Electricians' Text Book 

The panels contain the following parts: resistances, circuit 
breaker or overload release, no- voltage release, reversing switch (if 
required), starting arm and contacts, and necessary field contacts 
when necessary for variable speed motors. 

In this panel, the automatic overload release is in the nature of 
an ordinary spring-operated circuit breaker having the release 
mechanism operated by a positive hammer blow, and should open 
the circuit in case of overload under any condition. The overload 
device must be such that it will not operate by short-circuiting or 
opening the circuit of the retaining magnet of the no-voltage re- 
lease, and must be provided with renewable arcing contacts of 
carbon. 

Controllers. 

A controller is an arrangement for making the proper electrical 
connections between the main supply lines and a motor, so as to 
control the direction and speed of rotation. It is used for the con- 
trol of heavy currents in motors of above 10 horsepower and finds 
extensive use in such equipments as turret turning, gun elevating, 
rammers, ammunition hoists, boat cranes, deck winches, and in 
service generally where there is required continuous starting and 
stopping, and changes of direction and speed. 

A typical controller is shown in Fig. 148. It consists essentially 
of the following parts : 

The frame with cover; cylinder or cylinders; contact fingers; 
blow-out magnet; arc deflector; star-wheel, cap-plate, and handle. 

Frame. — The frame is of cast iron provided with a removable 
cover, in most cases made of sheet iron, but in some cases made of 
brass. 

Cylinder. — The cylinder is supported in bearings in the frame, 
and is operated by means of a suitable handle. On this cylinder 
are carried contacts suitably insulated from the shaft and from 
each other, arranged to make the necessary combinations for the 
control of the motor. The outside surface of these contacts is 
cylindrical and extends through only a portion of the circumfer- 
ence. In the center of this cylinder is a shaft which serves the 
purpose of supporting and operating the cylinder and also serves 






Motor Starting and Controlling Devices 341 




Fig. 148.— B-28 E Controller. Gen. Elec. Co. 



342 Naval Electricians' Text Book 

as a part of the magnetic circuit afterwards described. Upon this 
steel shaft is supported, either a wooden cylinder or a cylinder of 
specially made composition. On the outside of this are held cast- 
ings made of brass, which, in the case of the wooden cylinder, are 
fastened by means of screws, and in the case of the composition 
cylinder they consist of hollow cylinders entirely surrounding the 
special insulating composition, which by application of heat has 
been made to firmly fill the interior of the hollow cylinder and 
secure it to the shaft. In most cases, all those contacts which are 
to be electrically connected, are made in one casting, there being, 
consequently, a less number of castings on the cylinder than there 
are contacts. The projections on this casting, after being turned to 
a true cylindrical surface, are supplied with copper contact rings 
generally about 1 inch in width and J inch in thickness, which have 
been shaped to a true cylindrical form, and are fastened to the 
projections by means of two or more screws. These contact rings 
are thus made removable, so that in case of burning or of any injury 
to them, they may be replaced by new ones. 

Contact Fingers. — On the wooden block supported by the frame 
are several contact fingers, insulated by the block from each other, 
and from the frame. These fingers are stamped from copper, and 
are held in position by springs and adjusting screws, so that when 
the cylinder is rotated its contact rings will make firm contact 
with the fingers, the springs of which give sufficient pressure to 
insure a good electrical connection. The contact fingers are sup- 
plied with binding posts in which wires or cables are fastened, 
making the necessary connections between the line switch, motor, 
rheostat, and solenoid brake if used. In some cases these wires are 
carried directly out through the back of the frame, being insulated 
from it by rubber bushings, and in other cases the leads are carried 
down inside of the frame and brought out through a hole in the bot- 
tom. The fingers are fastened to their bases by means of small 
screws which readily permit of replacing any which may be in- 
jured. The adjusting screw is provided with a check nut, so that 
the screw will not jar loose, after the finger has once been adjusted. 
The finger bases are fastened to the wooden block by means of 
screws and the wooden block is fastened to the controller frame in 
a similar way. 



Motor Starting axd Controlling Devices 343 

Blow-Out Magnet. — In order to reduce the burning of the con- 
tacts which would naturally result to some extent from the opera- 
tion of the controller, a magnetic circuit is provided which has the 
effect of instantly breaking the electric arc formed when any circuit 
is broken. This circuit is produced by means of a spool or coil 
surrounding the lower end of the cylinder shaft. In addition a 
steel pole piece is supported over the fingers, being connected 
magnetically at the bottom of the shaft, so that a magnetic circuit 
is formed, consisting of the shaft, bottom of controller frame, and 
pole piece, the circuit being completed by the air space between the 
pole piece and the shaft, forming a magnetic field along the ends 
of the fingers. There is, of course, some magnetic field on the other 
side of the controller cylinder, between it and the back of the con- 
troller, but only that portion formed between the pole piece and 
the shaft is used in blowing out the arc. 

In some controllers, the magnetic blow-out spool does not sur- 
round the cylinder shaft, but has a separate core cast to the back 
of the controller, to which is attached a pole piece covering the 
contact fingers. In this case the magnetic field is produced between 
the pole piece and the back of the controller, the cylinder being in 
this field, and concentrating the magnetism on a line between the 
pole piece and the shaft, which line is near the ends of the contact 
fingers. 

In other controllers, the magnetic blow-out spool is a long nar- 
row coil surrounding the tip of the pole piece and carried just over 
the line of the fingers. This serves to concentrate the magnetism 
along the line of the finger ends where the arcing takes place. In 
the connections of the controller the winding of this spool is in 
series with the armature of the motor, so that whatever current 
passes through the armature also passes through the blow-out coil, 
and produces the necessary magnetism, which is therefore approxi- 
mately proportional to the amount of the current used. 

Arc Deflector. — In order to more thoroughly insulate the fingers 
from each other and from the cylinder and pole piece, strips of 
fire-proof insulating material are provided extending between the 
fingers and pole piece, with division plates extending from this 
plate between the fingers themselves and in some cases an addi- 



344 Naval Electricians' Text Book 

tional plate is provided between the finger bases and the cylinder. 
These insulating pieces prevent the arc, when thus formed, from 
being blown from one finger to the next, thus making a short 
circuit, which might otherwise occur and thus impair the effective- 
ness of the controller. 

Star-Wheel. — In order that the operator may judge of the posi- 
tion of the cylinder while operating it, without looking at it, a 
wheel is fastened to the cylinder shaft containing several notches 
or teeth, which engage a roller, supported on the end of the pawl 
which is pressed against the star-wheel by means of a spring. As 
the cylinder is rotated this pawl offers some resistance to the move- 
ment of the handle, and as it moves into the notches the effect is 
plainly felt by the operator, who should leave the controller handle 
only in the position shown by this pawl and star- wheel, because it is 
at these points that the fingers make the best contact with the 
cylinder. It should not be left at intermediate points. Also the 
star-wheel gives the additional advantage of making a quick break 
at the time of passing from one position to another, as the tension 
of the spring helps turn the cylinder after the roller has passed the 
point between two notches. 

Cap-Plate. — At the top of the controller is a cap-plate contain- 
ing stops to limit the motion of the handle and points to show 
the position of the cylinder. In some places this cap-plate is made 
of brass, in order not to interfere with the magnetic circuit and in 
other cases merely to form a more finished appearance. On some 
controllers the cap-plate is provided with a notch into which a 
latch on the handle will fall when the cylinder is turned to the off 
position, so that the operator when quickly stopping a motor will 
not carry the handle past the off position and reverse the motor. 

Handle. — The handle consists of a brass lever having a hole in 
its hub, made to fit the end of the shaft and allowing it to be easily 
removed, and carrying at its outer end a wooden revolving piece 
making it more convenient to operate. On some controllers a 
thumb-latch is attached to the lever, which is controlled by a pin 
passing through the center of the wooden piece, allowing the latch 
to be released by pressing on the pin. The latch is pressed down by 
a spring so as to engage the notch on the cap-plate when turned to 
the off position. 



Motor Starting and Controlling Devices 



345 



This particular type shows the cylinder to be operated by the 
meshing of gear wheels, the smaller of which is turned by an oper- 
ating wheel on top of the controller. 



B- 28 -CONTROLLER 

LOWER HOIST 




Fig. 149. — Developed Controller. 



Developed Controllers. 

In order to more clearly understand the diagrams of connections 
to be given under the application of motors, a so-called developed 
controller is shown in Fig. 149. 

This shows the development of the circular contact rings on a 
plane surface, with the indication of the contact fingers and method 
of connecting the resistances of the rheostat. 



346 Naval Electricians' Text Book 

All black lines and surfaces are conductors, the contact rings 
being indicated by the broad heavy lines and the contact fingers by 
circles. Where small white circles are shown on a black back- 
ground, they indicate contact fingers resting on the contact rings. 

It must be remembered that all contact fingers are stationary 
while the contacts are moved by the motion of the cylinder. In 
the above illustration a clockwise motion of the handle would re- 
sult in all the contact rings to the right of the row of fingers 
moving to the left as there viewed, and all the others on the other 
side moving to the left. A contrary motion of the cylinder would 
produce opposite motion of the contact rings. 

Contact is made between finger and ring when the ring is moved 
so that the finger rests and presses firmly on it. Connectors con- 
necting together contact rings move with them. 

Classes of Controllers. 

There are three general classes of controllers designed according 
to the kind of work they are to perform. Those made by the 
General Electric Company, which finds almost universal use on 
shipboard are arbitrarily designated as the E, B, and P types. 

R Controllers. — The R controllers are rheostatic in their method 
of operation, and are used for the purpose of starting, stopping, 
reversing and controlling the speed of motors. They are particu- 
larly adapted for motors designed to carry a load in either direction. 
In this type of controller the combinations are such that when the 
cylinder is turned to the first position in one direction, the circuit 
contact rings on the cylinder make connection with corresponding 
contact fingers, connecting the motor armature and field to the line, 
and having in its circuit the rheostat connected to the controller. 
On further rotation of the cylinder, the rheostat is gradually short- 
circuited, until at the last position of the cylinder the rheostat is 
entirely out of circuit, the motor then attaining its maximum speed. 
On returning the handle to its original position, this rheostat is 
again introduced into the circuit, and the motor slowed down and 
stopped. When the cylinder is turned in the opposite direction, 
the same effect is produced with the rheostat, but the direction of 
current through the armature, but not through the field, is reversed. 



Motor Starting and Controlling Devices 



347 



A developed form of a typical R controller is shown in Fig. 150 
used on turret gun rammers and formerly used for gun elevating. 
The motor is a series motor, the lower two lines on the left are the 
armature leads and the upper two are the series field leads. It 
will be seen how the controller connects them in series. 



R-28-D-CONTROLLER 



BACKWARD 



RHEOSTAT 
P.R. 

-o- 




Fig. 150. — R-28 Controller. 



to switch 
(Developed.) Gen. Elec. Co. 



B Controllers. — The B controllers are those which are designed to 
give electrical braking. By this the electrical solenoid brake used 
in some cases is not meant, as that is simply a mechanical brake 
electrically operated. But in the B controller the motor is made to 
run as a generator by the momentum of its armature or load, and 
in this way reduces its speed or stops itself. There are two kinds of 



348 Naval Electricians' Text Book 

B controllers; in one kind the various combinations are made on a 
single cylinder, while in the other kind, the braking effect is ob- 
tained by means of a second cylinder independently operated. In 
both kinds of these controllers the contacts are arranged so that in 
hoisting a load the operation is exactly the same as on one side of 
the E controllers, but on acting as a brake controller for lowering 
a load, or for carrying very light loads, a different combination is 
made, so that the rheostat to which the controller is connected, in- 
stead of being in series with the armature and gradually short- 
circuited as the armature is brought up to speed, is connected across 
the line in shunt with the armature. 

This controller is built to put in operation the Day system of 
control as further described under Motor Control in a previous 
chapter. 

A developed form is previously shown in Fig. 149. 

P Controllers. — This type of controller is used where the voltage 
of the generator is to be varied in order to obtain a change of 
speed of the motor. It is radically different from other controllers 
both in design and in system of control, although it retains the gen- 
eral features of all controllers, but the proportion and arrangement 
of its contacts are quite different. In its method of operation it 
introduces resistance into the field circuit of the generator in order 
to vary the voltage at the motor armature. The fields of both gen- 
erator and motor are separately excited, and the brushes of the 
generator directly connected to the brushes of the motor through 
the reversing contacts on the controller cylinder. Under these con- 
ditions a variation in the field of excitation of the generator pro- 
duces immediate change in the voltage impressed on the motor 
armature and a consequent change in the speed of the motor. 

The motor is reversed by turning the controller handle in the 
opposite direction from the off position, the contacts on the con- 
troller cylinder being so arranged that resistance in the generator 
field circuit is varied the same as before, but the direction of the 
current through the armature is reversed, thus reversing the direc- 
tion of rotation. At the off position the armature is short-circuited 
through a resistance, causing it to act as a generator and generate 
current and thus absorb energy. This produces a powerful braking 



Motor Starting and Controlling Devices 349 

effect and brings the armature to a quick stop. The suddenness 
of the stop may be regulated by adjusting the resistance thus intro- 
duced into the armature circuit. 

The P type of controller is used for turret control, both under 
the original Ward-Leonard system, in which the field of the main 
ship's generator was controlled, later in the motor generator sys- 
tem, in which the generator field of the motor generator was con- 
trolled, and still later in the rotary compensator system in which 
the fields of two machines are controlled. All these systems will 
be described later. 

The electrical connections of a controller of this type will be 
described later under Motor Applications. 

Circuit Breakers. 

General Description of Circuit Breakers. — The automatic circuit 
breaker is a device for automatically opening a circuit when the cur- 
rent exceeds the maximum amount desired. It is ordinarily ad- 
justed by means of a spiral spring, the tension of which may be 
varied ; the current at which the circuit will be opened being indi- 
cated on a scale near the spring. 

The point at which the circuit breaker is opened is located in 
such a position that the arc is easily destroyed and any damage 
caused by the arc may be repaired by replacing the injured parts. 
In other words, a circuit breaker is simply a switch which, when 
released by an electrically controlled latch, is thrown open by a 
spring. The essential parts of the circuit breaker consist of the 
arc-rupturing device, the main contacts, the resetting device and 
the adjusting and tripping device. 

Circuit breakers in general are of two kinds, depending upon 
the method employed for rupturing the arc. They are: 

1. Magnetic blow-out, in which the arc is extinguished by a 
strong magnetic field. 

2. Carbon break, in which the arc is ruptured at a secondary set 
of carbon contacts, which may be easily renewed. 

Magnetic Blow-Out Circuit Breakers. — Magnetic blow-out cir- 
cuit breakers, made by the General Electric Company, are known 
as Type M., Form Q., and Type M., Form L., the difference between 



350 Naval Electricians' Text Book 

them being in matters of design and not in the principle of opera- 
tion. They are single-pole instruments. 

The different sizes of these circuit breakers are distinguished by 
their carrying capacity rating, such as M. Q. 100/175. The first 
number of the rating is the minimum current that will automatic- 
ally open the breaker, and the second is the maximum continuous 
carrying capacity, but the breaker may be set to open at 50 per 
cent above this. This rating may be based on the continuous 
carrying capacity or the intermittent carrying capacity of the cir- 
cuit breaker. 

Carbon Break Circuit Breakers. — The carbon break circuit 
breaker, known as Type C, Form D., is a double-pole instrument 
consisting of two single-pole automatic switches mounted on one 
base. These may be set separately, but should both release together. 
The special advantage which this type has over the single-pole 
circuit breaker is that the switches may be independently closed and 
a short circuit or overload, which may develop when the last one is 
thrown in, will open the first one and protect the circuit. 

The different sizes of these circuit breakers are distinguished by 
their carrying capacity rating, as already described for the magnetic 
blow-out circuit breakers. 

M. Q. Circuit Breaker. — The M. Q. circuit breaker is shown in 
Fig. 151. The contacts at which the circuit is made or broken are 
located at the upper part of the base, where they are enclosed by 
two iron plates which form the poles of a powerful electromagnet 
in series with the line situated at the lower left-hand corner. The 
contacts themselves are composed of two flexibly mounted fingers 
on each side of the break, and are connected, when the circuit 
breaker is set, by a copper segment which revolves around the cen- 
tral pivot, forming a wiping contact with them. 

Above these contacts there is a rectangular fiber box, open at the 
top and bottom, in which the arc is broken. There is one metal- 
burning block above and connected to each pair of fingers, to which 
the arc is transferred as soon as formed, thus preventing the fingers 
from being burned and so disabled for further use. These burning 
blocks are renewable. 

The arc which is formed when the circuit breaker opens is located 



Motor Starting and Controlling Devices 



351 




o 



H 



352 Naval Electricians' Text Book 

in a strong magnetic field, which compels it to elongate towards the 
top opening until it is ruptured. 

The re-setting device consists of a handle projecting towards the 
lower right-hand corner, which is thrown off by a spiral spring at 
the center, and which, when forced in position by hand, is locked 
by a latch operated by a tripping device. 

The tripping device consists of a swinging armature held away 
from the pole of the magnet by a spiral spring, the tension of which 
may be adjusted to allow the circuit breaker to open at the desired 
current. When the magnet becomes strong enough to attract this 
armature against the tension of the spring, the latch releases and 
the circuit breaker opens. The circuit breaker may be tripped by 
hand by forcing the armature towards the pole piece. 

In order to inspect the contacts, the front pole piece may be 
removed by taking off the hexagonal nuts holding it. The front 
of the insulation box below may also be removed, leaving all the 
working parts exposed for examination, or repair. The illustra- 
tion given shows the parts removed. 

M. L. Circuit Breaker. — The M. L. circuit breaker is like the 
M. Q. a single-pole instrument. This type of circuit breaker is 
shown in Fig. 152. It is made with two coils, one of which fur- 
nishes a means of automatically tripping the breaker on overload, 
the other furnishes the magnetic field to blow out the arc. When 
the circuit breaker is closed, these two coils are connected in mul- 
tiple, but in opening, as soon as the laminated brushes are out of 
contact with the contact studs, the blow-out coil only is in circuit 
and a very strong magnetic field is produced which blows out the 
arc formed at the secondary contacts and opens the circuit. 

The main contact consists of an S-shaped set of copper leaf con- 
tacts which complete the circuit when closed against the contact 
studs at the lower right-hand corner of the base. A secondary set 
of contacts in multiple with the above is located in the strong 
magnetic field formed by the blow-out coil. 

The secondary contacts consist of two fixed contacts, located in 
the fiber box or chute in which the arc is broken and between the 
poles of the blow-out magnet, and a movable contact, carried on the 
end of a rod and forced up from below to close the space between 



Motor Starting and Controlling Devices 



353 



the fixed contacts. These secondary contacts are renewable and 
should be carefully attended to in order to assure their being in 
good condition, as poor secondary contacts will cause the main 
laminated brush to be destroyed. 

When an arc is formed at the secondary contacts the strong 
magnetic field causes it to elongate towards the top opening of the 
fiber chute until it is nurtured. 




1BONT CONNECTED. 



BACK CONNECTED. 



Fig. 152. — Form M. L. Magnetic Blow-Out Circuit Breakers. 
Gen. Elec Co. 



The re-setting device consists of the handle projecting towards 
the lower right-hand corner, which is thrown off by a spiral spring 
at the center and which, when forced in position by hand, closes 
first the secondary contacts by forcing upward the rod which carries 
the moving contact, then the main S-shaped brush contacts, and is 
locked in position by a latch operated by a tripping device. 

The tripping device consists of a swinging armature pivoted over 
the pole of the tripping magnet located at the lower left-hand 
corner. It is held away from the pole of the magnet by a spiral 



354 



Naval Electricians' Text Book 



spring, the tension of which may be adjusted to allow the circuit 
breaker to open at the desired current. When the magnet be- 
comes strong enough to attract this armature against the tension 
of the spring, the latch releases and the circuit breaker opens. The 
circuit breaker can be operated by hand by pulling down on the rod 
connected to the armature. It is calibrated by screwing up the 
calibrating screw until the disc near the spring is opposite the 
desired mark on the scale. 




P IG 153. Type " C ", Form K, Carbon Break Circuit Breakers, 

250 Volts, 1000 Amps. Closed. Gen. Elec. Co. 

Type " C " Circuit Breakers.— The type " C " circuit breaker, so 
called because the arc is ruptured by carbon auxiliary contacts, is 
shown in Fig. 153, and consists of two stationary contacts with a 
laminated brush, and secondary copper, and tertiary carbon con- 
tact which will close by means of a handle operating through a 
toggle joint. 



Motor Starting and Controlling Devices 



355 



It is held closed by a latch which is tripped by an armature, the 
latter being when the current exceeds a predetermined amount. 

This breaker is made single or double pole, that shown in the 
figure being single pole. 

In the smaller sizes, a coil is employed to carry the current for 
moving the tripping armature, while in the larger size, such as is 
shown in the print, the armature simply forms a swinging section 
of the magnetic circuit, the stud passing through this circuit and 
forming a tripping coil of one turn only. 




Fig. 154. — CB-17 Motor. Gen. Elec. Co. Detailed Parts of Band Brake. 



Solenoid Brakes. 

These are used on motors particularly designed for hoisting and 
lowering weights and are intended to check the speed or even stop 
the motor and hold the load in case of failure of current, and to 
prevent the load from falling and running the motor as a generator. 

They are used on all turret ammunition hoists, on chain ammu- 
nition hoists, on whip hoists, boat cranes, and deck winches. 

The solenoid brake is macle in two types: 

1. An electrically-operated band brake. 

2. An electrically-operated friction disc brake. 



356 



Naval Electricians' Text Book: 



The former type is fitted to chain ammunition hoists, and with 
a modification to deck winches and the latter, with modifications, to 
the other form of hoists. 

The Solenoid Band Brake. — The band-brake type consists essen- 
tially of the following parts : wheel, band, solenoid, and lever, and 
is shown in detail in Fig. 154. The wheel is a flat-faced pulley 
located on the armature shaft. The brake band consists of sheet 
steel lined with leather and surrounds the wheel, one end being 
attached to a lever near the end upon which it pivots, and the other 
end of the band secures to the outside of the solenoid case. On 
the free end of the lever is attached the solenoid plunger which 




Fig. 155. — Assembled Solenoid Band Brake. Gen. Elec. Co. 



ordinarily acts under gravity, thus drawing the band tightly around 
the wheel and preventing the armature from turning. When this 
weight is lifted the band is released and the wheel turns freely. 

The solenoid consists of a spool the core of which is attached to 
the brake lever and lifts the same when energized. Consequently, 
when a current is passing through the coils, due to the operation of 
the controller, the brake is automatically released and remains 
open until the circuit is broken. 

The brake should always be kept free to move, as it is the ulti- 
mate safety device in case other means of control fail. 

The wheel should be kept clean and free from oil or dirt, the 
leather on the band in good condition, and the band adjusted so that 
it does not bear upon any point of the wheel when lifted. 



Motor Starting axd Coxtrollixg Devices 



357 



The connection of the solenoid should be examined whenever the 
condition of the motors is inspected. 

An assembled solenoid band brake fitted to an armature shaft 
is shown in Fisr. 155. 




SECTION E-F-G-H 



KEY TO SECTIONS 



_j 






CAST IRON STEEL BRONZE INSULATION BABGITT 



Fig. 156.— ED-108, Form A Disk Brake. Gen. Elec. Co. 



The Disc Brake. — The automatic disc brake shown in section in 
Fig. 156 and in exploded view in Fig. 157 consists of a cast-steel 
frame, an electromagnet, steel armature, discs, annular rings and 
springs. 



v) 

V .5 




l I 

6 ib 



5 

1 



Motor Starting and Controlling Devices 359 

Frame. — The frame is a steel casting consisting of a base carry- 
ing a barrel of sufficient depth to receive the discs, rings and 
armature. Four tobin bronze studs provide a support for the 
electromagnet and there are two keyways diametrically opposite to 
receive the steel keys on which annular rings have an easy sliding 
fit. A hole is cast in the back of this barrel through which the 
extended motor armature shaft projects. 

Electromagnet. — The electromagnet is a steel casting with suit- 
able lugs which support it on the frame. Brass nuts draw the 
magnet to the frame, making a water-tight joint. 

A coil slot, annular in form, is provided in the casting in which 
the winding is secured by type metal. 

Suitable spring pockets equally spaced are drilled to receive the 
helical compression springs. 

Armature. — The armature is a steel disc of a sufficient cross- 
section to carry the magnetic flux without excessive leakage. Four 
tobin bronze pins are tapped into the armature and project into 
recesses in the magnet. This construction keeps the armature from 
rotating while permitting easy motion parallel with the motor 
shaft. 

Annular Rings. — The rings are of cast iron and have a sliding 
fit on the keys in the frame, which prevent their rotation. 

The outside diameter of the rings is slightly less than the inside 
of the barrel. The inside diameter is carried out to a point where 
the friction is most advantageous and yet provides a sufficient cross- 
section to insure against an excessive wear or heating. 

Suitable oil slots are provided to secure a uniform lubrication. 

Discs. — The discs are of bronze and have suitable hubs which are 
keyed to the motor shaft. 

These discs have an easy motion parallel with the shaft but 
being keyed thereto must revolve with it. 

Holes in the discs relieve atmospheric pressure and add to the 
convenience of removing the discs from the shaft. 

The outside diameter of the discs is slightly less than the rings, 
to secure a clearance from the keys in the frame. The width of the 
friction face is thus the difference in radius between the outside of 
the disc and the inside of the ring. 



360 Naval Electricians' Text Book 

Compression Springs. — The springs are helical in form and are 
wound of the best spring steel, copper plated. They resist the 
maximum compression without permanent set or injury. 

Coil. — The winding consists of insulated copper wire, form 
wound, and wrapped with four thicknesses of varnished cambric 
and two thicknesses of linen binding. 

The ends of the coil are soldered to terminals located in a water- 
tight connection box in the magnet, tapped for conduit, through 
which the brake leads are to be taken to the coil terminals. 

The inside back of the frame is finished to a suitable diameter 
and thus becomes a friction face. Adjacent to it is a bronze disc 
keyed to the armature shaft, then an annular ring keyed to the 
frame, then another disc keyed to the armature shaft and thus 
throughout the series. Each ring is keyed to the frame and its 
adjacent disc to the motor shaft. 

The electrical connections are so arranged in the controller that 
the motor circuits are simultaneously made with the brake coil 
circuit. 

Thus when the controller is thrown on the first position the brake 
coil energizes the magnet, which draws the steel armature disc 
toward it, at the same time compressing the helical springs. Thus 
all pressure on the friction faces of the discs is relieved and the 
motor starts readily. 

There is a sufficient clearance provided between each set of fric- 
tion faces to reduce the running friction in the brake to a mini- 
mum, a lubrication of these surfaces is provided by an oil hole in 
the top of the frame and a drain hole in the bottom which permits 
a change of oil. Best operation is obtained with a minimum 
amount of lubrication. 

When the controller is turned to the " off " position the brake 
coil circuit is opened and the springs immediately force the arma- 
ture disc against the bronze disc keyed to the shaft and thus the 
pressure is transmitted to all the friction faces. Thus in coming to 
rest the armature shaft must carry the discs keyed to it through the 
friction of all the rings keyed to the frame, the friction face of the 
frame itself and the friction face of the brake armature. The spring 
pressure is sufficient to bring the motor armature quickly to a state 
of rest and yet not injure the friction faces of the discs or rings. 



Motor Starting and Controlling Devices 



361 



These brakes are designed to hold the load of the 12-ineh ammu- 
nition hoists plus 25 per cent. 

Magnetic Core Brake Type. — This brake consists of a disc, the 
periphery of which is a conical surface, and a stationary frame 
with conical recess within which the disc revolves with the conical 
surfaces in close proximity. Spiral springs force the conical sur- 
faces together, and a coil winding imbedded in the stationary frame 
opposes the action of the springs and releases the brake when cur- 
rent is on the coil. The disc is loosely keyed to the shaft extension 
so that it is free to move lengthwise of the shaft thus allowing the 
brake to be set and released without interfering with the end play 
of the shaft. 




Fig. 158. — Brake Coil Connections for Hoisting. 



The coil consists of two separate windings in parallel. These 
coils are connected up so that one coil is short-circuited when the 
armature receives full voltage. This gives a strong pull for re- 
leasing the brake and cuts down the current through the brake 
coils one-half under running conditions. 

Brake Windings. — The connections of the brake winding are 
made so that in hoisting one coil is in parallel with the starting 
resistance and the other in parallel with the armature as shown 
in Fig. 158. 

On starting the motor M for hoisting, as current is switched to 
the starting resistance SR, there is a greater difference of potential 
between the ends of this resistance than between the armature 
terminals, as the armature has not started to turn, so consequently 
coil A receives most of the current, while B is practically short- 
circuited by the armature. Coil A lifts the plunger of the solenoid 



362 



Naval Electricians' Text Book 



and opens the brake, bringing the core of the plunger and the 
solenoid yoke close together. 

As the motor armature attains speed, and develops counter 
E. M. F., the difference of potential between its terminals becomes 
greater than that of the terminals of the starting resistance and 
coil A, so the current in B gradually increases while that in A de- 
creases, and at full speed as the armature terminals have practically 
the full voltage of the line, B is fully energized while A is short- 
circuited, and B is now holding the brake open. This arrangement 
cuts down the current to that required to operate the brake through 
coil B, which is considerably less than the energy required for two 
such coils in series. 



S R 



Pig. 159. — Brake Coil Connections for Lowering. 



For lowering the connection is made as shown in Fig. 159. 

On starting the motor for lowering, coil A is energized as before 
for hoisting, and remains so, the circuit being established to the — ■ 
main by the connecting conductor from the starting resistance. 
As the armature current is now reversed, the current through B is 
also reversed, this tending to demagnetize the solenoid, working 
against A. Current through B increases as the counter E. M. F. 
increases, and if the coils had the same number of turns, one might 
neutralize the other, but coil B is made of smaller wire, so has less 
magnetizing power and coil A has still enough, magnetism to hold 
the brake clear. 

If the motor acts as a generator, the E. M. F. generated causes 
current through B which holds the brake released, but as it slows 
down, the current becomes less and less and finally the brake is set 
by the action of the opposing springs. 



CHAPTEK XVIII. 
APPLICATION OF MOTORS. 

Turret-Turning Equipment. 

Up to the present time there have been four different systems 
used to electrically control the turning of turrets of our ships of 
war. These are generally referred to as the Ward-Leonard System, 
Motor Generator System, Rotary Compensator System and Variable 
Speed System. 

Ward-Leonard System. 

Principles of Operation. — The turret is turned electrically, the 
method of the speed control of the driving motors being especially 
adapted for fine regulation. 

There are ordinarily two electric motors. These motors are 
governed in speed and direction by a controller, situated under the 
sighting hood. The operator has only to turn his controller handle 
from the " off " position in a clockwise or a counter clockwise direc- 
tion accordingly as he wishes the turret to move, and the motors 
will drive the turret as desired, the speed of travel being dependent 
upon the amount which the handle has been displaced. 

The method of control depends upon the fact that the speed of a 
motor armature running in a constant magnetic field is proportional 
to the volts impressed upon its brushes. Therefore, by conveniently 
varying this voltage the speed of the motor is changed. 

By this method each turret requires one independent generator 
for the supply of the turning motors, but the switchboard is so de- 
signed that any of the several generators may be used for any turret. 

The fields of the motors and of the generator are separately ex- 
cited from the switchboard bus bars and are consequently inde- 
pendent of the voltage generated by the armature of the generator. 

The field rheostat on the generator panel board is cut out and 



364 • Naval Electricians' Text Book 

in its place another rheostat in the turret operated by the controller 
is used, the generator field wires being carried to the turret for this 
purpose. The series coil of the generator is shunted by a switch, 
the object of this being to allow the series coil to have a slight 
effect in building up the voltage of the generator so that the turret 
may start more promptly than if it were dependent on the shunt 
coil alone. 

The armature terminals of the generator are connected through 
the necessary switches, etc., directly to the armature terminals of 
the motors. The motors are usually in multiple. As the engine 
drives the generator armature at a constant speed the volts delivered 
by it to the motor armatures are approximately proportional to the 
shunt field excitation, and consequently the speed of these arma- 
tures, and of the turrets, is directly controlled by the operator in 
the turret. 

This statement is correct, regardless of the mechanical resist- 
ances encountered, up to the load which causes the engine to 
slacken materially in speed. 

The current required is dependent upon the turning moment 
necessary to overcome mechanical resistance, and will not vary 
greatly at any constant speed, regardless of what that speed may be. 

The circuit is so arranged that either motor may be electrically 
cut out and the other motor be operated to the extent of its 
capacity. 

If, when the turret is in motion, the controller is turned to such 
a position that the armatures would be driven as motors at a 
lower speed than that corresponding to the speed of the turret, the 
turret will drive the armatures, which will immediately generate 
current and absorb energy, bringing the turret down to the speed 
of the armatures when running as motors. 

When the controller is placed on the off position, the brushes of 
the motors are connected through a low resistance, so that the 
armatures would generate large currents if revolved, thus requiring 
much expenditure of energy, which would be greatly increased by 
the mechanical connections from the turret, and thus electrically 
locks the turret. This condition does not hold unless the motor 
fields are excited. 



Application of Motors 365 

The controller, in addition to operating the generator field 
rheostat, also sends the current to the motor armatures in the 
direction to give the rotation required. 

There is an ammeter in each armature circuit, so that the opera- 
tor may know when either motor is running under unusual load. 
An automatic circuit breaker opens the armature circuit of both 
motors in case of an overload. 

The brushes of the motors and the generator are connected by 
the armature leads and are independent of all other connections. 

The field of the generator is separately excited from the constant 
potential bus bars, and this circuit is extended to the rheostat 
located in the turret. The motor fields are also excited from these 
bus bars. 

The reason for separately exciting the generator field is to cause 
it to respond immediately to a change of the rheostat and thus avoid 
the delay required in building up a self-exciting generator. The 
motor fields are separately excited in order to give a constant exci- 
tation, which could not be obtained from the driving generator, as 
the pressure at the motor brushes will vary according to the desired 
speed. 

Thus the person operating the rheostat controls the speed of the 
motor, which will remain constant at any point until the resistance 
is changed. 

In the actual installation the same hand wheel which controls 
the rheostat also controls the direction of rotation of motor, so that 
the operator who is training the turret has complete command of 
the direction and speed of movement. 

Fig. 160 shows the entire connection of this system in which one 
main generator is used to turn a turret, as originally installed, and 
by the aid of the description of the electrical connections the differ- 
ent connections can be traced. 

The controller used is of the P. type, mentioned under the head 
of Classes of Controllers, Chapter XVII. 

Electrical Connections. — The electrical connections are shown 
on Fig. 160. The armature connections of the motors are brought 
to the fingers connected with the second wide segment from the bot- 
tom after having passed through the blow-out coil and the fingers 



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Fig. 160. — Electrical Connections of Ward-Leonard System. 



Application of MotopiS 367 

connecting with the upper wide segment. The main lines are 
brought to the binding posts attached to the fingers of the two re- 
maining wide segments. From each one of the main lines and 
armature leads, is branched a circuit through an auxiliary rheostat, 
and connected to the single fingers. It will be noted that the auxil- 
iary contacts are longer than the main contacts, so that in rotating 
the cylinder in either direction from the off position, the auxiliary 
contacts touch their corresponding fingers a little before the main 
contacts make connection, and breaks the connection later when 
the controller is being turned off. This provides a gradual making 
and breaking of the main circuit in the operation of the controller, 
and reduces the amount of arcing that would occur at the main 
contacts if the auxiliary contacts were not used. When the cylinder 
rotates on the first position the main connections have been made 
and the current passes as follows : From the switchboard through 
the circuit breaker, to the lowest finger, to contact rings, to the lead 
to the motor armatures, through the switches and motor armatures, 
and back to the other side of the generator armature circuit through 
the second wide ring from the top. At this time the field of the 
generator is separately excited through the field rheostat which is 
connected to the controller, the leads of which are marked El to R9. 
While this rheostat is in the field circuit, the potential of the gen- 
erator is at a minimum, but on turning the controller cylinder to 
the second position, the section El to E2 of the rheostat is short- 
circuited, the field current thereby increasing and the potential of 
the generator being raised, which, of course, increases the speed of 
the motors. The further rotation of the cylinder short circuits 
more of the field rheostats, until on the 9th or last position, the 
entire field rheostat is short-circuited, and the potential of the 
generator reaches its maximum. On returning the cylinder to 
the off position, the field rheostat is again connected in the field 
circuit, reducing the potential of the generator, and therefore the 
speed of the motor, until just before the off position is reached, 
the main contacts leave their fingers, thus forcing the current to go 
through the auxiliary rheostat, reducing the current considerably, 
and when the off position is reached, the two main lines are entirely 
disconnected from the motor armatures, the circuit of the armature 



368 Naval Electricians' Text Book 

being closed through a brake rheostat by means of triple fingers 
on the back of the controller, this bringing the armatures to a sud- 
den stop. The circuit is made as follows: Armature terminals 
to blow-out spool, to line ring, to left-hand brake fingers, to brake 
rheostat, to right-hand brake fingers, to other terminals of arma- 
ture. The suddenness of the stop of the armature may be regu- 
lated by adjusting the brake rheostat. On turning the controller 
in the other direction from the off position, the same results are 
obtained except that the direction of current through the armature 
is reversed, thus reversing its direction of rotation. 

Motors and Gearing. — In order to make the understanding of the 
turret- turning system complete the following description is given 
of the motor gearing by which the turret is revolved, and as a 
general guide to the construction of the gearing of all turrets. 

There is one motor located on each side of the turret below the 
floor. They revolve in' opposite directions, both driving through 
bevel gears to one shaft which runs across the turret. This shaft 
carries at each end a right-hand double-threaded worm, and each 
worm engages with a worm wheel at the top end of a vertical shaft. 
At the lower end of the vertical shaft of each of the worm wheels is 
a pinion which meshes with the circular rack inside of the barbette, 
thus driving the turret. 

The worm wheels are connected to the vertical shafts by friction 
clutches which can be adjusted by nuts above to carry the desired 
load, but to slip if it be exceeded, in order to prevent damage to 
the driving mechanism due to an excessive overload such as would 
occur when firing one gun, or in the case of impact of a shell on the 
outside, tending to produce rotation independently of the motors. 

These friction clutches consist of fifteen flat discs, alternately of 
brass and steel, the brass discs being loosely keyed to the outer case 
and the steel discs fastened to the inner case which carries the worm 
wheel in the same manner, these discs being pressed together by the 
action of ten helical springs. These springs are held in the outer 
casing of the vertical shaft, and their pressure is adjusted by 
sliding a covering casting along the shaft by means of a large re- 
cessed nut and check nut at the top. 

The object of the cross shaft is to allow one motor to revolve the 



Application of Motors 



369 



P-10 CONTROLLER 

LEFT.-^ ^RIGHT 
l2718SI20l17ll3l 9J5 II*" 7\ XI I S ) 9 'l3'17l8olS3'27l31 |35l 33 



FIELD 
RHEOSTAT 



LOW 
RESISTANCE 




COMMUTATOR END 



DISCHARGE 
RESISTANCE 



G.S. SHUNT 

MJVUUI-, 

SERIES FIELD 

MAAAAr 

SHUNT FIELD 

,w/wwv\r 




GENERATOR 

Fig. 161. — Variation of Ward-Leonard System. 



370 Naval Electricians' Text Book 

turret by driving both pinions should the second motor be electric- 
ally or mechanically cut out, and also to permit one motor to 
revolve the armature of the other motor, in case the latter should 
fail electrically, through the bevel gears instead of through the 
worm wheel and worm, which would be the case if the cross shaft 
were not employed. 

Connections of Generator, Motors and Controller for Turret-Turn- 
ing System Using Combined Generator and Motor 
Field Control. 

In the diagram of electrical connections shown in Fig. 160 the 
system of control embodies only variation of the field of the gen- 
erator, but in that shown in Fig. 161, there is combined generator 
and motor field control. Another difference lies in the fact that in 
the first system the turning motors are in parallel while in that 
shown in Fig. 161 the motors are in series. 

A form of controller used with this system of control is shown 
in Fig. 162. 

Electrical Connections. — The function of the controller in con- 
necting the current from the main generator to the armatures of 
the two motors in series is readily seen from the diagram of con- 
nections, the armature current in all cases being indicated by the 
heavy lines. The current through the armature motors is reversed 
by moving the contact pieces by the controller hand in opposite 
directions. It will also be noticed that the motor armature termi- 
nals are short-circuited through the brake rheostat when the con- 
troller is in the off position, so if the motors are given any motion 
independent of the generator current, they will act as generators, 
which, generating current through the low resistance will absorb 
power and bring them quickly to rest. 

Current for the generator and motor fields is taken from power 
lines on the ship as indicated in the lower right-hand corner. This 
controller is designed to control both the current through the gen- 
erator and motor fields, and the separate operation is as follows : 

Generator Field. — Current flows from the left-hand line lead to 
and around the generator field, thence to the terminal on the con- 
troller resistance marked 50. Between each one of these numbered 



Application of Motors 



371 



blocks is a resistance. The current flows from block 50 through 
all the resistances to block 1, from there to the finger contact 
marked El, thence to the contact ring over it and from there back 
to the line lead. This is the 
circuit in the off position 
and the generator field is 
excited when the line field 
switch is closed. As the 
controller is moved, say to 
the right, the contact ring 
on which rests El, moves to 
the right and makes contact 
with E2. This results in 
short-circuiting the resist- 
ance from 4 to 1, and the 
total resistance in the gener- 
ator field is reduced by that 
resistance. Further move- 
ment to the right brings the 
contact rings in connection 
successively with E3, E4, 
etc., each time cutting out 
some resistance, until the 
ring makes contact with 
E19, when the only resist- 
ance in the generator field is 
that between 50 and 49, and 
at that time, there is maxi- 
mum voltage at the gener- 
ator terminals and the mo- 
tors are running at their 
maximum speed due to con- 
stant excitation. Up to this 
point, this constitutes the 
speed control as far as 
changes in the voltage of 
the generator, and the volt- 
ages impressed on the motor terminals, are concerned. 




Fig. 162.— P-10 Controller for Combined 
Motor and Field Control. 



372 Naval Electricians' Text Book 

Any further motion beyond that which connects R19 throws the 
lower finger of the two above Rl off its contact ring, when the 
generator field circuit is completed through finger R20 (the rheostat 
resistance for the generator being completely short-circuited), as 
the upper left-hand contact ring now connects with R20. This 
ring is connected with the one just below it, and the connection to 
the return field lead is made through the upper finger of the double 
fingers above Rl. 

Motor Field. — Current flows from the left-hand line lead, as for 
the generator field to the left-hand terminal of the three shown 
between the two motor fields, where it divides, going through and 
around the fields in parallel, to the right terminal of the three, and 
thence to finger Rl. From here current flows to the contact ring 
above #1 and then back to the field line lead. This gives constant 
excitation to the motor fields and it remains constant during the 
movement of the controller up to the time that the generator field 
resistance is being cut out ; that is, up to the point when the contact 
finger above Rl leaves its contact ring. At this point, the contact 
ring is just on R19, when the motor field current from Rl flows 
through all the contact rings to R19, then to block 49, through the 
resistance to 50, then to R20, and back to the field line as explained 
for the generator field. 

Any further motion to the right throws El 9 off its contact ring 
increasing the resistance in the motor field circuit to that between 
50 and 47. Continued motion to the right, gradually adds resist- 
ance to the motor field circuits, weakening their fields and causing 
consequent increase of speed. This continues until all the resist- 
ance that was cut out of the generator field in the first half of the 
operation is thrown into the motor fields. Thus allows a double 
change of voltage ; in the first operation the voltage of the generator 
increases due to cutting out of its field resistance while the motor 
fields are constant and in the second operation, the voltage at the 
terminals of the motors increases due to cutting in resistance in 
their fields, while the field of the generator remains constant. 

The middle terminal of the three between the motor field 
switches connect to the return side of the field lead. 

An inspection of the diagram will show that when the switches 



Application of Motors 373 

are closed, this connection plays no part, as it is broken from the 
field leads by an insulated clip in the switches, but when either 
switch is open, the connection indicated by the arrows is made 
which has the effect of cutting out, or short-circuiting the controller 
rheostat, and the turret is then turned by one motor* with a con- 
stant excitation. 

Motor-Generator System. 

The system of turret turning just described requires the sole use 
of one of the main generators, no matter what reserve power it may 
have. This is due of course to the varying voltage produced at its 
terminals by variations of the exciting current of its shunt field. 

In the motor-generator system, a motor generator is interposed 
between the main generator and the turning motors, the voltage of 
the main generator remaining constant, and the remainder of its 
power may be used on other constant potential circuits. 

A constant voltage is delivered by the main generator to the ter- 
minals of the motor of the motor generator, and the field of the 
motor is excited from constant potential mains. The generator 
armature of the motor generator has the same speed as the motor 
armature, and its field is varied by a suitable controller and 
rheostat. 

The voltage developed by the generator will depend upon its 
speed and field excitation, so the voltage delivered to the terminals 
of the turning motors will be altered by any change in its speed or 
in its field. The speed will be practically constant and changes in 
the generator field are made by the controller and rheostat. 

Specifications for Motor Generator Sets. 

As a general guide to the requirements of motor generator sets 
the specifications prepared by the Navy Department for Turret- 
Turning Motor Generator Sets is given : 

Specifications for Turret- Turning Motor Generator Sets Issued by the 

Navy Department. 
(To oe Rated oy the Kilowatt Capacity of the Generator.) 
1. To consist of a direct current 120-volt motor and a direct current 
130-volt generator, with common frame having suitable supporting 



374 Naval Electricians' Text Book 

feet. Both armatures to be mounted on a common shaft, with commu- 
tators toward the shaft ends, or between the armatures, as the con- 
tractor may desire. Unless otherwise specified, rotation to be right 
hand — i. e., clockwise, facing motor end. 

2. Sets to be of the semienclosed type with suitable openings in end 
shields only, for ventilation, inspection, and adjustment of brush rig- 
gings and for inspection of commutators. Openings other than in end 
shields are not permissible. All openings to be fitted with covers, 
which shall consist of rigid metal frames fitted with perforated sheet 
brass of at least No. 16 B. & S. gauge, or with the brass wire mesh; 
wires to be at least No. 16 B. & S. gauge. The sheet metal or wire mesh 
must be securely fastened to the frames and must be able to stand 
heavy shock without tearing away. They shall preferably be of slightly 
convex form to give additional strength. If sheet metal is used the 
perforations shall be circular, of not less than three-sixteenths inch nor 
more than one-fourth inch diameter. If wire mesh is used the wires 
shall be laid not less than three-sixteenths nor more than one-fourth 
inch center to center. 

3. Covers to be capable of being readily opened and closed; this to 
be done without use of tools. To be readily fastened when closed in a 
positive and secure manner, such as will not permit their becoming 
loosened or displaced by continued vibration. 

4. Drain cocks shall be fitted to the frame to permit drawing off 
water or oil which may collect on the interior, provided the construc- 
tion is such as to form pockets in the frame. 

5. Frame to enclose two separate magnetic circuits, each having four 
or more equally energized poles. 

6. Shaft to be of steel, with accurately fitted journals. To run in 
two bronze self-oiling bearings, one at each end of the frame. To be 
provided with suitable means to prevent oil from bearings working 
along to armatures. Bearings to be provided with sight glasses on oil 
chambers and suitable drains for removal of oil at will. 

7. Frame to be divided horizontally, the two parts to be bolted to- 
gether, to permit ready removal of armatures and field coils. 

8. Generator field to be compound wound in a manner which will 
adapt the machine for furnishing power for variable voltage control. 
The series winding is intended to compensate for the resistance drop 
in armature and leads to turret-turning motors due to sudden increase 
in load, and shall be such as to give not less than 30 volts with shunt 
field disconnected, 200 amperes flowing through generator armature, 
and set running at normal speed. A readily adjustable shunt of ap- 
proved design shall be connected across the terminals of the series 
winding. 

9. Sets to be designed for speed not exceeding 1500 revolutions per 
minute — the design to be with a view to minimizing weight and overall 



Application of Motors 375 

dimensions; speed variation between no load and full load and from 
full load to no load not to exceed 6 per cent of normal. 

10. Commutator bars or segments to be supported on a shell which 
must be directly attached to the spider or keyed to the shaft; bars to 
be of hard drawn copper, finished accurately to gauge; insulation be- 
tween bars to be of carefully selected mica, gauged to uniform thickness 
and of such hardness as will wear evenly with the commutator bars. 

11. Bars to line with the shaft and run true; to be securely clamped 
by means of bolts and clamping rings. There shall be no openings by 
which any foreign substance can get to the interior of the commuta- 
tors. The commutators and brush rigging must be designed to permit 
handling heavy and fluctuating curents up to as high as 150 per cent 
in excess of normal full load current, both with full shunt field and 
very weak shunt field, all with brushes in fixed position. 

12. Brushes to be of carbon; current density not to exceed 40 amperes 
per square inch; each brush on a stud to be capable of separate removal 
or adjustment, and means shall be provided for simultaneously shifting 
all brushes; brush holders to be of the sliding shunt-socket type; 
springs to be of material other than steel and must not be relied upon 
to carry the current. 

13. Finished armatures to run true and be balanced both electrically 
and mechanically. The completed sets must run at all loads without 
noise or vibration. 

14. A name plate to be fitted to each motor generator in a conspicuous 
place, containing the following data: 

MADE FOR 

Bureau of Equipment 

by 

(Name of maker here.) 

Req. No. — . Date — . Rating — . 

Factory No. — . Volts — . Amp. — . 

Field (Gen.) — . Amp. — . Ohms. — . 

Factory number to be also stamped on the frame under the name 

plate. 

15. Separate name plates shall be fitted to indicate which is the 
motor end and which the generator end. 

16. The overall dimensions must not exceed the following: 15 kilo- 
watts, 56 by 27 by 27 inches long; 25 kilowats, 68 by 28 by 28 inches 
long. 

17. The design must be such that when installed in confined spaces, 
with but 4 inches clearance at each end, the upper parts of the field 
frames can be lifted and the armatures removed or replaced. 

18. There shall be no wires carried to the exterior of the frames, 
but the internal arrangement shall be such that the connecting wires 



376 



Naval Electricians' Text Book 



can be suitably carried to their proper contacts with the machine 
assembled. These wires will be carried in conduit pipes which will tap 
directly into the lower part of the frames; conduit bosses shall be fitted 
on each side of each end, but the frames need not be tapped by the 
builder unless specifically required. Two armature leads and one 
field lead will pass to the motor end; two armature leads and two field 
leads will be taken from the generator end. On each side of motor end 
and of generator end there shall be two bosses for l^-inch iron pipe 
size and one for %-inch iron pipe size. 



Connections of Panel and Rheostat for Starting Motor-Generator 
Sets for Turret-Turning Equipments. 

These are shown in Fig. 163. 




MOTOR GENERATOR 

Fig. 163. — Connections for Starting Motor-Generator Sets for Turret 
Turning. Gen. Elec. Co. 



Application of Motors 377 

The two supply mains on the left run, one to each of two distri- 
bution boards, and the motor line is connected to the hinge end of 
a two-pole, double-throw switch, so current from either board may 
be used. 

The field of the generator is controlled by a controller and 
rheostat similar to that shown in Fig. 160. 

The starting resistance for the motor is of slightly different 
design from any of those previously designed, but presents no new 
principle, and the connections are easily traced. 

In another system of installation of the motor generator, speed 
control is effected by changes in the fields of the generator of the 
motor generator and the turning motor, similar to that shown in 
Fig. 161, in which the generator shown may be considered as the 
generator of the motor generator. 

Rotary Compensator System. 

This system is designed and supplied by the General Electric 
Company. It consists of a small motor driving the turret through 
a high gear reduction by means of an electric clutch, and a large 
motor directly connected to the turret through a lower gear reduc- 
tion, the gear reduction being so designed that the turret will be 
turned at about the same speed by the small motor when operating 
at maximum as by the large motor when operating at minimum 



The electric clutch will disconnect the small motor mechanic- 
ally at the time the armature of the large motor is electrically con- 
nected to the source of power, the large motor being continuously 
turned when the turret is in motion, while the small motor will be 
turning at variable speed without load when the large motor is 
turning the turret. 

The connections of this system are shown on Fig. 164. The 
variation in speed of the large and small motors together with the 
change in gear reduction above mentioned, will give delicate speed 
control of turret between approximately J° per minute and 100° 
per minute. 



378 



Naval Electricians' Text Book 




Applicatiox of Motors 



379 



There will be severe-five speed positions of the controller, the 
approximate speed of the turret at various positions being shown 
on curve sheet (Fig. 165). 



100 








r ' - 


























































90 




































































































































i 70 

S 

a. 


































































OL 

d 

UJ 60 

Q 

z 


































































1- 

UJ 

a. 
j§ 50 

i- 

B. 


































































O 

D 
111 

S 40 
Q. 
CO 






















































/ 












30 






















/ 






























/ 


/ 












20 




















/ 






























/ 


/ 














10 








TfW 


SITIC 


N PO 


INT. 




/ 






























V 


f 






























CONT 


roll 


ER P< 


)INTS 















10 20 30 40 50 

Fig. 165.— Speed Curve. 



60 



70 



80 



380 Naval Electricians' Text Book 

The variation in speed of the machines will be upon the variable 
voltage system obtained from a rotary compensator. This compen- 
sator consits of two armatures mounted upon the same shaft, re- 
volving in two separate magnetic fields, each supplied with series 
and shunt windings, the connections of the separately excited shunt 
fields being so made that the strength of the fields are varied by 
means of a shunt resistance operated by the controller, the voltage of 
one armature being raised when the voltage of the other armature 
is reduced. The small motor armature is placed in multiple with 
one armature winding of the compensator and is increased in speed 
from a minimum to maximum, at which position of the controller 
the voltage of the second armature is at a minimum, allowing the 
large motor to be started under these conditions, and thereby in- 
creasing the speed of the turret to the above-mentioned maximum, 
while the second armature is cut out mechanically from operating 
the turret. 

The two motors are connected to the system through a com- 
mutating switch (Fig. 166) designed for three positions to meet 
the following conditions : 

1. Both motors operating the turret. 

2. Small motor only operating turret (large motor cut out). 

3. Large motor only operating turret (small motor cut out). 

In order to give a little greater speed variation when the small 
motor or the large motor is operating independently, than is ob- 
tained from either motor when they are operating together, field 
resistance is inserted so that under normal conditions the small 
motor will run at full field, and the large motor at slightly weakened 
field, but when running separately the small motor will run at 
weakened field to give approximately 6J° per minute of turret 
maximum, with a corresponding increase in the minimum speed, 
and the large motor will run at a speed to give approximately 4J° 
per minute of the turret with a corresponding reduction in the 
maximum speed, the speed of the turret at transition from small 
to large motor under normal conditions being approximately 5J° 
per minute. 

These field rheostats are inserted in the motor fields by suitable 
connections at the commutating switch. 



Application of Motors 



381 



The controller (Fig. 167) is designed to give the above maximum 
speed in each direction by a movement of the cylinder of 170° 




Fig. 166.— 52-A Commutating Switch. Gen. Elec. Co. 



either side of the " off " position, the motion of the cylinder in 
either direction from the " off " position to the starting position 
for the small motor being 18°. 

The clutch is designed to drive the turret from the small motor 



382 



Naval Electricians' Text Book 



and will operate promptly and effectively. It will be provided with 
a resistance to be placed in series with the coil in order to give 




Fig. 167.— P-13 A Controller. Gen. Elec. Co. 



more prompt action, and allow adjustments to meet the conditions 
of installation. 

The construction of the rotary compensator is considered in 
Chapter XX, Dynamo Electric Machines. The motors present no 



Application of Motors 383 

■unusual features and are similar in construction to those described 
in the chapter on Service Motors. 

Rotary Compensator Starting Panel. — The starting panel for 
the rotary compensator will be of the flame-proof type. 

It will consist of an insulating panel carrying at the top a double- 
pole,, single-throw line switch, below which will be located a starting 
rheostat switch with no-voltage release. 

The starting resistance will be mounted behind this panel, and 
terminals for leads will be suitably located on the panel. The 
entire panel and resistance will be mounted in a water-tight, cast- 
iron box with the cover held in position by screws and wing nuts, 
and provision will be made so that the main line and starting 
switches can be operated from the outside of the box without 
removing the cover. 

Magnetic Clutch. — This consists of two steel discs, upon one of 
which the worm gear will be mounted by the purchaser, and the 
other carrying the energizing coil and collector rings. Both discs 
are mounted upon a sleeve, which is rough finished inside to be 
bored and splined by the purchaser to fit the shaft, upon which it 
will be keyed. 

The first disc rotates freely upon this sleeve, being held by col- 
lars from longitudinal motion, while the second disc is keyed to 
the sleeve and arranged so that it can move longitudinally and thus 
release the clutch when the energizing circuit is open. 

The collector rings are mounted upon a hub projecting from this 
first disc, upon each of which two carbon brushes bear, these being 
provided with the brush holders which are fastened to the turret at 
the time of installation. 

At 10 E. P. M. this clutch will transmit 150 per cent of full- 
load torque of the small motor, and will stand full current, which 
can pass through it in series, with its resistance at 120 volts, with- 
out temperature rise exceeding 50° C. at the end of this time, 
measured by resistance. Or, in other words, it will deliver 2J 
H. P. at 10 E. P. M. 

A rheostat in series with the coil is furnished in order to obtain 
more prompt action, and reduce the voltage at the terminals to 
approximately 60 volts. 



384 Naval Electricians' Text Book 

Controller. — The P-13-A controller is designed to control two 
turret motors operating through, different gear reductions so that 
the motion of the turret shall be absolutely positive in its action and 
in complete control of the operator. 

It will allow the turret to move by small increments and be 
turned at seventy-five definite speeds in either direction, there being 
a large number of intermediate speeds available between each pair 
of above-mentioned speeds. 

Each speed will be continuous and uniform for the complete dis- 
tance through which the turret can be turned. 

Classification. — This controller is classified as P-13-A and it con- 
sists of the following parts: 

Frame. — The frame is of cast iron with feet at the bottom. The 
cap-plate is detachable and fastened to the frame by flat-headed 
screws. This cap-plate will be marked to indicate " off " position 
of the controller and the full " on " position of the controller, with 
two marks showing the high-speed running position of the small 
motor and the low-speed position of the large motor, the space be- 
tween these marks being the movement of the controller cylinder 
necessary to ensure transition between the two motors. 

The front cover will be of sheet iron held in position by hinge 
bolts, two on each side, so that it can be swung to either side or 
removed entirely if desired. 

A back cover of sheet iron will be provided for protection of the 
terminals, the studs of which project through the top of the con- 
troller frame. 

Cylinder. — The cylinder carrying the contact segments will be 
supported upon a steel shaft insulated from it by a special 
compound. 

Shaft. — The shaft will be of steel, extended at the top for the 
attachment of a hand wheel or operating shaft and provided with 
a water cap. 

The bottom of the shaft extends beyond the controller for the 
attachment of the automatic stop. This shaft carries at the top 
and just below the cap-plate a star-wheel with one notch at the 
"off" position into which a pawl operated by a spiral spring 
will fall. 



Application of Motors 385 

Contact Fingers and Segments. — The upper half of the cylinder 
will consist of contact segments for controlling the armature cir- 
cuits of the two motors, the clutch circuit, and one lead from the 
compensator field circuit, these being mounted upon special insu- 
lated supports. 

One row of easily renewable and adjustable fingers will make 
connections. 

Field Connections. — Connections to the field rheostat of the com- 
pensator are made through a carbon brush, connected to the finger 
on the lower segment of the upper part of the cylinder above 
described, and bearing upon the ends of a commutator mounted 
concentric with the shaft and supported from the back of the con- 
troller frame. 

Leads attached to the lower ends of these commutator segments 
pass to a connection board at the bottom of the controller, to which 
the taps to the field rheostat are made. 

The above-mentioned carbon brush being attached at the junction 
of the two compensator shunt fields, controls the voltage at the two 
ends of the compensator by its position and consequent division of 
resistance of the two parts of the rheostat, which are in multiple 
with the two shunt fields. 

Since the resistance of this carbon brush forms a part of the 
shunt circuits to the two fields, its exact position relative to the two 
segments upon which it bears affects the field currents of the com- 
pensator, and as this brush can take an indefinite number of posi- 
tions in passing from one segment to the next a corresponding 
indefinite number of speeds of both motors can be obtained. 

The commutator is cross-connected, allowing the brush during 
the first half of its travel to pass over the rheostat taps in one 
direction and during the second half of its travel to pass across them 
in the opposite direction, this being necessary in order to give the 
proper speed control of the two motors. 

The carbon brush is driven through the train of gears making it 
turn at approximately double the angular speed of the cylinder, so 
that when the main shaft has turned approximately one-half a 
revolution in order to give full speed of turret in one direction, the 
brush travels nearly 360°, the difference being due to the dead 
spaces in the commutator. 



386 Naval Electricians' Text Book 

Terminals. — The terminals for the main contacts at the top of 
the cylinder consist of studs to which the leads can be attached, 
and which pass through the back of the controller into the finger 
bases where they are held by set-screws. - This will allow the large 
wires to be brought up behind the controller and covered after 
installation by the sheet-iron case previously described. 

The leads from the commutator will pass through an annular 
opening in the bottom of the controller frame, and be attached to 
studs mounted upon an insulated connection board, to which the 
leads from the rheostat can be attached, thus allowing the commu- 
tator board to be readily disconnected from the resistance leads. 
The connection board will be provided with a sheet-metal covering 
to protect the terminals from external injury. 

Electric Brake. — The main cylinder is connected so that when it 
is in the " off " position, the armatures of the large motor and small 
motor will both be short-circuited, thus producing an electric brake. 

Commutating Switch. — The commutating switch (Fig. 166) is 
similar, in general construction, to the turret-turning controller, 
but as it is only designed to make desired connections for various 
conditions of operation and not to open circuits carrying current, 
it varies in some details from controller construction. 

Classification. — The commutating switch consists of the follow- 
ing parts : 

Frame. — The frame is of cast iron, furnished with four feet at 
the back for attaching to the support. The cap-plate is of brass, 
detachable, and fastened to the frame by flat-headed screws. It will 
be marked " small motor," " small motor and large motor," " large 
motor," and will be provided with a brass handle for turning the 
cylinder to the desired position. 

The cover is of sheet iron, held in position by hinge bolts, two at 
each side, so that it can be swung to either side or removed entirely 
if desired. 

Cylinder. — The cylinder carrying the segments will be of wood 
impregnated by paraffin supported upon a steel shaft. 

Shaft. — The shaft will be of steel provided with a star-wheel at 
the top with a pawl for holding the cylinder in the desired position. 

Contact Fingers and Segments. — The contact fingers and seg- 
ments will be similar to those furnished with standard controllers. 



Application" of Motors 387 

Terminals. — The leads to the above fingers will pass through an 
opening in the bottom of the frame behind the cylinder, provision 
being made for convenient attachment to the' fingers, which are 
located in two rows, one at each side of the frame, it being neces- 
sary to remove the cylinder from the frame in order to attach the 
leads to the finger bases. 

Rheostats. — There will be fonr rheostats in the field clntch cir- 
cuits of this equipment. 

Each rheostat consists of a cast-iron frame supporting a fiber 
panel on which are mounted the terminals of the resistance, these 
terminals being marked as shown on Fig. 164. 

Several terminals to allow adjustment of resistance after instal- 
lation are provided. The rheostat for use with the compensator 
and controller is provided with a considerable number of extra 
terminals, the resistance being so graduated as to give a speed 
curve to the turret approximately as shown on curve sheet. 

The resistance will be of the " EC " or Enclosed Card type. 

Circuit Breakers. — There will be supplied two automatic mag- 
netic blower circuit breakers, one for the large motor and one for 
the small motor. 

Each of these circuit breakers will be enclosed in a water-tight 
cast-iron box which will be furnished with bosses on the sides to 
be drilled out for conduit, and will have projecting handles, so that 
the breakers can be set or tripped from the outside, without open- 
ing the box. 

Elementary Principle of the Rotary Compensator. 

The foregoing description of the actual apparatus will make 
clear the connections in the elementary diagram of connections in 
Fig. 168. 

A and B are the armatures of the rotary compensator, and it 
must be remembered that they are mounted on the same shaft, so 
turn at the same speed, and each has its own separate field 8 and 
S'. L x and L 2 are the armature leads from the starting panel and 
l t and l 2 are the field leads from constant potential source. 

Motor armature D is in parallel with machine B and C in parallel 
with A. D corresponds to the small motor in the previous de- 



388 



Naval Electricians' Text Book 



scription and C to the large motor. R is a resistance between the 
shunt leads and connected by an arm H to the junction of the two 
fields of A and B. 

If the starting switch is closed and the fields of both A and B 
energized with arm H in mid-position, both armatures of A and B 
will run as motors, their armatures being in series. During this 
stage of operations, neither C nor D is connected to their armatures. 

The fall of potential through armatures A and B will be equal 
and the sum of their brush differences of potential will be equal to 
the difference of potential in the leads L ± and L 2 . This will be 
the case because the fields of each are equally excited. 





Fig. 168. — Elementary Connections of Rotary Compensator. 



If G?! = difference of potential across brushes of A, 

fy ii ii ii ii ii it T> 

g = " " « " line, 

E 1 = Counter E. M. F. due to A, 
E 2 = " " " B, 

C a — armature current, 
r,a= " resistance of A, 



Then at any time 



" B. 



£ x — C a r ia = E, 



adding 



® — C a (r ia + r 2a ) =E ± + E 2 . 



Applicatiox of Motors 389 

Suppose the field of S is short-circuited by moving the arm II 
so as to cut out all resistance, then the excitation of S will fall to 
practically zero, in which case 

E 2 = 0, 
or 

e 2 = C a r 2a 
H 1 — E 1 = C a r ia . 

As the field of S' is fully excited, E x is very nearly to Q x , and 
their difference is small, therefore C a is small, and C a r 2a , the differ- 
ence of potential across B is very small. The operation of decreas- 
ing the resistance in parallel with S has been to lower the voltage 
of B and raise that of A. 

As the resistance of R is gradually cut in by moving the arm H 
up, as shown, the fall of potential across B gradually increases, 
because the field S increases and consequently E 2 increases. E x 
must therefore decrease and the fall of potential across A decreases 
in such a ratio as to keep the sum of Q x and (£ 2 equal to (?. 

"When the arm H is in its mid-position the fields are equally 
excited and the fall of potential across A and B is each equal. 
Further movement of H will more or less short circuit S', when by 
similar reasoning it is seen that the fall of potential across A de- 
creases while that of B increases. 

D is the small motor connected in parallel with B and at any 
time it has impressed on its brushes the voltage across the brushes 
of B. Consequently, if connected at the low voltage, as the voltage 
of B increases D will gradually speed up. At a certain point when 
the voltage of B has increased to near its maximum value and A 
decreases to its minimum value, the armature of C is connected to 
A. Its gearing is such that it takes up the speed of the turret just 
where B was disconnected, and the resistance is now varied in the 
reverse sense so that the voltage of A increases while that of B 
decreases, thus causing the motor C to speed up. 

When D is running with a low voltage impressed on its brushes, 
it may be that the current is not sufficient to drive the three arma- 
tures, in which case more current will flow from the line and B 
may act as a generator supplying the extra needed current. When 



390 Naval Electricians' Text Book 

D has a high voltage, E 2 is high and probably all the current comes 
from the line through A. 

Variable Speed Gear. 

The mechanical device known as variable speed gear has been 
installed for turret training and will be nsed for gun elevating, 
and from its description it will be seen that it may be applied to 
any apparatus in which a large variation of speed is required. 

The variable speed gear as furnished by The Waterbury Tool 
Company, is a machine for transmitting rotary torque at variable 
speeds and in either direction without steps or abrupt gradation, 
while the source of power rotates continuously in one direction 
without any necessary change of speed. This source may be an 
engine of any kind, an electric motor or any revolving shaft or 
mechanism from which it is desired to transmit power. There are 
no gears within the transmitter itself, and, as the medium of trans- 
mission is oil, which is practically incompressible, the driving is 
very positive. 

Functionally the machine consists of two mechanisms, called 
respectively the A end and the B end (Fig. 169). The function 
of the A end is to receive the power by being coupled, geared and 
belted to the source of power and to transmit it to the B end by 
transferring oil from a low-pressure chamber to a high-pressure 
chamber. In other words, the A end is an oil pump : 

It is the function of the B end to act as an oil engine operated 
by the pressure of the oil pumped to it by the A end, and exhausting 
the oil back into the low-pressure side of the A end. 

The two ends A and B are made up of exactly similar parts, 
although these parts are not necessarily of the same dimensions. 
Moreover, as the controlling is usually done entirely on the A end, 
the B end is not equipped with the controlling parts unless for 
some special purpose. 

The two ends A and B may be built as separate mechanisms con- 
nected by conducting pipes, or they may be combined into one 
machine, the two parts being separated by a mid-plate. A mid- 
plate becomes two end-plates when the machine is constructed as 
two separate mechanisms. 



Applicatiox of Motors 391 

Important Parts and Their Functions. 

Case. — An outer case, usually a steel or bronze casting, encloses 
the working parts and forms a reservoir, which should be kept en- 
tirely full of oil at all times. The case also supports the tilting- 
box trunnions which bear the whole thrust and torque of the driving 
power. In some types of construction the shaft passes through the 
end of the case where it has one of its bearings, while the other 
bearing is in the mid-plate. In other types, where the A ends 
and B ends are separated into different mechanisms, the shaft may 
pass through and have its bearing in the end-plate only. 

Shaft. — The shaft in the A end receives the power and the shaft 
in the B end gives up this power. On the shaft and rotating with 
it are the cylinder barrel and the socket ring. 

Cylinder Barrel (Tigs. 169 and 170). — The cylinder barrel is 
keyed to the shaft by two swiveled keys, allowing the barrel a very 
slight movement like that of a universal joint and also allowing 
it to move freely a short distance along the shaft under the pres- 
sure of two springs, which are only strong enough to slide the 
barrel along the shaft and keep it pressed lightly against the face 
of the end-plate, or mid-plate, as the case may be. When the 
machine is transmitting power, the pressure of the oil itself, by a 
peculiar construction of the cylinder ports, keeps the faces of the 
barrel and plate in contact with just force enough to prevent exces- 
sive leakage. In the barrel are the cylinders arranged parallel with 
the shaft, and in the cylinders, piston operate. Each piston is con- 
nected with the socket ring by a connecting rod. Each connecting 
rod consists of a shaft with a ball on each end, one ball being held 
in a socket in a piston, the other in a socket in the socket ring. 
The sockets are lubricated through a hole extending lengthwise 
through the connecting rod, the balls and the end of the piston, 
which is in communication with the oil under pressure. 

Socket Ring. — The socket ring is connected rotatively with the 
shaft by an intermediate ring and trunnions forming a universal 
joint. The universal joint must be so constructed as to permit 
the socket ring to rotate with the shaft, but at any angle to the 
shaft up to the maximum provided for in the designs, say 20 
degrees. The connection between the socket ring and the shaft 




n 1 LvELKEYNMI' ml/ V \LCT ^^ j i 



Pig. 16S-Variable Speed 



394 Naval Electricians' Text Book 

does not receive the end thrust of the oil pressure on the pistons, 
but it does transmit the whole torque/ in the A end from the shaft 
to the ring, in the B end from the ring to the shaft. The end 
thrust is against a large ball-bearing between the socket ring and 
the tilting box. 

Tilting Box. — The tilting box is a very important part of the 
mechanism inasmuch as the speed and direction of rotation depend 
upon the tilting of the box at different angles to the shaft. It 
swings on two trunnions which pass through each side of the case 
and so may be considered as a fixed part of the case itself, capable 
of being tilted on its trunnions at the will of the operator but inde- 
pendently of the shaft rotation. A worm wheel segment forms a 
part of the box of the A end, and engages with a control worm 
screw by which the box is tilted on its trunnions. The box of the 
B end may be equipped exactly like that of the A end, but generally 
the box of the B end is set at a fixed angle when the machine is 
assembled and no provision is made for a change of angle. In 
designs having the shaft extend through the case, there is a hole 
through the bottom of the box through which the shaft passes and 
large enough to allow of tilting the box to its extreme angle without 
coming in contact with the shaft. Where the shaft passes through 
the end plate only, the box may have an entire bottom. 

The most important functions of the tilting box are two : first, 
to furnish a support for the ball thrust bearing against which the 
socket ring rotates; and, second, to vary the lengths and direction 
of the piston strokes by varying the angle of the tilting box with 
the shaft. 

Control Screw. — The control screw is a worm screw engaging the 
worm segment of the tilting box and having its shaft extend 
through the case. The turning of the control screw controls the 
speed and direction of the B end by determining the direction of 
flow and the quantity of oil supplied to the B end. The shaft of 
the screw passes through a ball in the wall of the case, allowing 
the screw to be adjusted into close mesh with the segment by an 
adjusting screw which extends through the end of the case and 
presses against the bearing block of the inner end of the screw shaft. 

Mid-Plate or End-Plate. — The mid-plate or end-plate (Fig. 171), 



Application of Motors 



395 





396 Naval Electricians' Text Book 

as the case may be, receives the cylinder barrel or barrels against 
one or each of its faces. The contact is a raised annular surface. 
In the barrel contact surface ports open from each cylinder. In 
the plate contact surface there are two long ports forming annular 
arcs diametrically opposite each other and opening into oil cham- 
bers or passages leading to corresponding ports in the other face of 
the plate or in the other end of the machine. When the machine is 
transmitting power, the pistons of the A end, moving by virtue of 
the angle of the tilting box, draw in oil from one of the chambers, 
and carrying it across the land which separates the two annular 
ports, force it into the other oil chamber ; the oil thus transferred by 
the A cylinders is carried back by the B cylinders. Each of the 
oil chambers of the plate is provided with check valves, called 
replenishing valves, admitting oil from the case reservoir to replen- 
ish leakage. In one of the chambers the oil is under pressure and 
holds the valve closed; in the other chamber the oil is not under 
pressure and oil from the case is free to pass up through the valves. 
If it were not for the replenishing valves, the leakage of oil past the 
pistons and between the surface of the barrel and plate would tend 
to create a vacuum in the low-pressure chamber. Which of the 
chambers is high pressure and which low is determined by the 
direction of rotation together with the direction of the angle of the 
tilting box. 

Applicability. — The machine is applicable as a transmission de- 
vice wherever there is an irreversible and constant source of rotatory 
power which it is desired to transmit at variable speeds and in 
either direction at will. As the changes of speed are perfectly 
smooth along a perfect curve in either direction from zero to the 
maximum without step or jump, it will be seen that its applicability 
covers a very wide range. Moreover, the speed of the B end is 
limited or restricted by the angle of the tilting box of the A end. 
The machine thus acts as a positive brake holding the speed of the 
B end under the absolute control of the operator. 

Efficiency. — The efficiency of the machine has been found by 
numerous tests to be more than 80 per cent when running under 
normal conditions. When the B end is running at very slow 
speeds, the efficiency is considerably less, but no matter at what 



Application of Motors 397 

speed the B end runs, the full torque due to the oil pressure is 
maintained, and the only limit to this torque is the strength of the 
machine to withstand the pressure, and the small leakage, which, 
although it becomes less, as the speed is reduced, yet at extremely 
slow speeds approaching zero and under heavy pressure, is large in 
proportion to the oil actually pumped, or in active circulation. 
Measurements made at half load and at full speed have shown a 
leakage of 2J cubic inches in an active circulation of 4800 cubic 
inches per minute. Very great smoothness and regularity of rota- 
tion are easily attained at speeds as low as one rotation of the B 
end in one minute. 

It should be understood that this leakage does not escape from 
the machine, but only passes from the high pressure side into the 
case reservoir, thence through the replenishing valves to the low- 
pressure chamber. 

Gun-Elevating Equipment. 

The two general systems used in this equipment are the direct 
system and the motor-generator system. 

In the direct system, the elevating motor armature is connected 
directly to the constant potential mains of the ship and the varia- 
tion in speed is obtained by varying the resistance in series with 
the armature. This does not allow of very fine control, and the 
present practice to obtain very small changes of speed is to use the 
motor generator between the power mains and the elevating motor, 
the field of the generator being varied to change the voltage im- 
pressed on the motor terminals. 

Direct System. — The first system is illustrated in Fig. 172 and 
the elementary diagram in Fig. 173. 

The equipment consists of the shunt motor, controller, rheostat 
and switch panel. The controller is of the R type (rheostatic con- 
trol) and arranged to give five speeds in either direction. It has a 
short-circuiting contact in the off position, closing the armature 
circuit and causing it to act as a powerful brake. 

The switch panel is provided with a double-pole, single-throw 
switch, a single-pole magnetic circuit breaker, and a discharge 






398 



Naval Electricians' Text Book 



R-28-K 
CONTROLLER 



STARTING 
EAJSEL 




Fig. 172. — Connections for Elevating Equipment of Turret Guns. 
Gen. Elec. Co. 




RHEOSTAT 

Fig. 173. — Elementary Diagram of Electrical Connections. 



Application of Motors 399 

resistance arranged to be cut into the field circuit when the field 
switch is opened. 

The rheostat is of the pressed-ribbon type previously described. 

Motor Gearing. — The mechanical connection between the ele- 
vating motor and the gun is effected by a series of bevel gears and 
shafting; one inclined shaft is threaded and on this shaft travels 
the block to which the gun-elevating rods are attached. 

An athwartship shaft is carried to the outboard side of the turret, 
and on its end is fitted a small sprocket wheel which can be driven 
by a sprocket chain from a second wheel, operated from a crank on 
the turret floor. This is worked by hand in case of electrical fail- 
ure of the elevating equipment. 

Motor-Generator System for Gun Elevating. — Motor generators 
are used for turret turning and gun elevating, the principles in each 
case being identical and for purposes of illustrating the general 
system connections are given in Fig. 174 for 8-inch elevating 
equipment. 

The elevating equipment consists of the motor generator, ele- 
vating motor, motor starting panel and speed-control rheostat. 

The starting panel contains a double-pole, single-throw switch, 
fuses, starting resistance and no-voltage release. The fields of the 
motor of the motor generator and of the elevating motor are excited 
by constant potential, while the field current of the generator is 
varied by the speed-controlling rheostat, thus changing the voltage 
at its terminals and at the motor terminals, consequently producing 
variable speed. 

The speed-controlling rheostat has been described in the chapter 
on Controlling Devices. It serves the double purpose of varying 
the speed and of changing the direction of rotation of the armature. 

While the direct method of gun elevating only permits of four 
or five different speeds, this method allows of any speed between 
the minimum and maximum. 

Gun-Loading Equipment. 

The electrical equipment for rammers of turret guns consisting 
of a motor, series wound, controller, rheostat and either a main 
line switch or circuit breakers. 



400 



Naval Electricians' Text Book 




Application of Motors 



401 



The ordinary R form of controller (rheostatic) is used and 
pressed-ribbon rheostat. Fig. 175 shows the connections of the 
equipment, showing five speeds each way for the rammer. Fig. 178 
is of later design, the principal differences being that it has two 
single-pole circuit breakers mounted in a cabinet and the backward 
motion of the rammer only has two speeds while forward motion 
has five. 



RIGHT GUN 



C.B.-15-A-1 
MOTOR 



R-28-D-CCNTROLLER 

BACKWARD FORWARD 

54321 123 45 




Fig. 175. — Electrical Connections of Gun Rammers. Gen. Elec. Co. 



The elementary diagram of connections is shown in Fig. 177. 

A view of the controller showing the method of mounting the 
resistances for the later type is shown in Fig. 176. 

The armature shaft carries a pinion which is loose upon it and 
which is driven by a friction clutch keyed to the armature shaft 
set up by means of a spiral spring so that any unusual torque on 
the pinion will cause the latter to slip freely on the shaft. This 
pinion engages direct on the gear on the rammer case. 



402 



Naval Electricians' Text Book 




Fig. 176. — Controller for Rammer Motor. 



LINE 



B.O. 



RHEO. 



AAW 



LINE 



C.B. 




Fig. 177.— Elementary Diagram of Gun-Loading Equipment. 



Application of Motoes 



403 



Friction Safety Clutch. — The pinion on the motor shaft is free 
to revolve on the shaft, except as it is held by the friction between 
it and the steel disc keyed to the shaft, which is pressed against 
the pinion by a steel spiral spring. So long as the friction between 
the composition pinion and the steel disc is sufficient to absorb the 
torque of the motor, this pinion drives the gear on the rammer, 
operating it. Whenever for any reason the motor takes an exces- 



CIRCUIT BREAKER CABINET 



BACKWARD 



FORWARD 
-1 Tit 

i r 




Fig. 178. — Electrical Connections of Gun Rammers. Gen. Elec. Co. 






sive current, developing a torque beyond the friction between the 
pinion and the disc, the armature shaft slips freely in the pinion. 
The friction between the panel and the disc is regulated by increas- 
ing or decreasing compression on the spring, which is done by set- 
ting up on the jam nuts on the end of the armature shaft. This 
clutch is an essential feature of the rammer apparatus, as other- 
wise very excessive currents might cause damage, or at least blow 
the fuses when the shell was finally pressed home in the bore of 
the gun. 



404 



Naval Electricians' Text Book 




Application of Motors 



405 



Ammunition Hoists. 

These are of three general types, viz., turret-ammunition hoists, 
chain-ammunition hoists and whip-ammunition hoists. 

Turret- Ammunition Hoists. 

The equipment for the latest type of control consists of a shunt 
motor fitted with disc pattern of brake, controller of the B type 
(electrical braking), motor armature rheostat, and a switch and 
circuit breaker cabinet. 

These are shown in Fig. 179, and the elementary diagram of con- 
nections for lowering in Fig. 180. For hoisting, the connections 




Fig. 180. — Elementary Diagram of Ammunition-Hoist Connections 

(Lowering). 



are the same with the exception that the rheostat is in series with 
the armature. The system of control is the Day system previously 
explained. 

In the controller the handle is arranged to turn the cylinder 
through bevel gears ; raising the handle directs the current through 
the motor to hoist the ammunition car and lowering it lowers the 
car. It is of the type described under the B rheostats with the 
resistance in series with the armature for hoisting and across the 
line for lowering, and the armature short-circuited when in the 
" off " position, producing powerful brake effect. 

The brake circuit is connected so that it is released when current 
is on and with a brake relay in parallel with the motor field, so 
that if the field current fails, the brake circuit is broken and the 



406 



Naval Electricians 7 Text Book 



brake set. To stop the hoist suddenly, it is only necessary to throw 
the handle to the off position quickly, which immediately opens the 
circuit and the brake is immediately set. Also, if the main circuit 
breakers open, due to overload, the relay circuit is broken, which 







Fig. 181. — 12-inch Ammunition-Hoist Controller. 



opens the brake circuit and sets the brake. This is shown in 
Fig. 180. 

An open view of a 12-inch -turret ammunition-hoist controller is 
shown in Fig. 181. 



Application of Motors 



407 




© & i> &_<§) &> 



ARMATURE- 






BRAKE 



r IELD 



Fig. 182. — Controlling Panel for Chain Hoist. Gen. Elec. Co. 



408 Naval Electricians' Text Book 

Chain- Ammunition Hoists. 

The electrical equipment consists of the motor with solenoid 
brake and its controlling panel. 

The electrical connections are shown in Fig. 182, and the ele- 
mentary diagram in Fig. 183. 

Solenoid Brake. — This is of the solenoid type previously de- 
scribed and consists of a brake wheel on the armature shaft and a 
leather-lined band operated by a lever and solenoid. The solenoid 
consists of a coil entirely enclosed in an iron shell, thus completely 
protecting it from external injury, while allowing it to be easily 
taken apart for -inspection. When current is on the coil, the lever 
arm is lifted and the brake released, and when current fails the 
lever arm drops and the brake is set. 



fuse c.b. °)f ER A L0 A AD RHEa 

UNE a □ — WV 




Fig. 183. — Elementary Diagram of Connections of Ammunition Hoist. 

From the diagram it is seen that the brake solenoid receives full 
voltage of the line from the controlling panel when the motor is 
running with full voltage on the armature. 

Mechanical Equipment. — Each hoist consists of a pair of endless 
chains, traveling over sprocket wheels, and reaching from the point 
of loading to that of delivery. These chains support between them 
carriages placed at proper intervals for receiving the ammunition, 
the whole being driven by an electric motor through a system of 
gearing. 

The armature shaft of the motor is geared to a counter shaft of 
the hoist which has a pinion on the other end,, engaging a gear on 
a shaft carrying the two sprocket wheels. The continuous chain 
belts pass over these sprockets and run up to two similar sprockets 



Application of Motors 409 

in a casting set in the deck at the point of delivery. These chain 
belts are connected at equal intervals by carriages on which the 
ammunition boxes are placed. The two bearings of the shaft for 
the lower sprockets can be moved along an arc of a circle having its 
center at the center of the counter shaft which is geared to the 
sprocket shaft. This permits the distance between the upper and 
lower sprockets to be adjusted to compensate for stretch and wear 
in the chain. The adjustment is made by means of two adjusting 
screws, with lock nuts, which push the bearings up or down. When 
the adjustment is made, the bearings are held in place by a lock nut. 
In order to prevent the possibility of the loads overhauling and 
running the hoist backwards in case the driving mechanism should 
fail, pawls are provided which allow the carriages to pass up, but 
will catch and hold them if they move down. When it is desired 
to lower ammunition, these pawls can be thrown out of action by 
means of a rod operated from the top of the hoist. This rod runs 
down the side of the hoist, and when revolved it raises the pawls 
and turns them back into pockets so that the carriages can 
descend without engaging them. A hand gear is provided in order 
that the hoist may still be operated if for any cause the driving 
motor fails. It consists of a hand crank located at a convenient 
place near the hoist and connected by an arrangement of sprocket 
wheels and chain to a clutch on the intermediate shaft. This 
clutch is operated by a hand lever, moving in the plane of the shaft, 
and is so constructed that when the lever is moved in one direction, 
the intermediate shaft is connected to the large motor gear and 
the hoist is electrically driven : but when the lever is moved in the 
opposite direction, the intermediate shaft is disconnected from the 
motor gear and is connected to the sprocket of the hand gear and 
the hoist is ready for hand drive. When the lever is thrown for 
hand drive, the intermediate shaft runs freely in the motor gear, 
and when it is thrown for electric drive, the shaft runs freely in the 
sprocket wheel of the hand-drive system. 

Whip Hoists. 

These are generally installed for hoisting ammunition for the 
secondary battery between decks or bridges, by means of rope whips. 



410 



Naval Electricians' Text Book 




Application of Motors 411 

Electrical Equipment. — Each equipment consists of an enclosed 
water-proof shunt motor, having its armature shaft geared to a 
drum shaft and operated by a single cylinder controller and 
rheostat. The diagram of connections is shown in Fig. 184 and 
the elementary diagram in Fig. 185. 

The armature shaft of the motor is fitted with a magnetic cone 
brake, so constructed that the friction is released as soon as the 
controller is turned to the hoisting or lowering position, but 
promptly operates as soon as the controller is turned to the off 
position, or current fails through any cause. 




Fig. 185. — Elementary Diagram of Connections of Whip Hoist. 

The controller is of the B type, and in lowering produces the 
braking effect of the Day system of control. The armature is also 
short-circuited on the off position of the controller. 

Boat Cranes. 

The electrical equipment of boat cranes present differences in 
their details but the electrical principles are the same. It consists 
generally of two iron-clad enclosed series motors, one for hoisting 
and one for revolving. In some installations there are two separate 
controllers, each in a separate casing, one for each motor, with 
separate circuit breakers mounted in separate boxes operated from 
the outside; and in others the two controllers and circuit breakers 
are all mounted in one case. 

The electrical connections are shown in Fig. 186 and the elemen- 
tary diagram of connections in Fig. 187. 

The controllers are the R type, the rheostat is of the pressed- 
ribbon type, and the circuit breakers of the MQ type. 






412 



Naval Electricians' Text Book 




o 



Application of Motors 



413 



LINE 



V\AAAtO 



C.B. 




RHEO. 



Fig. 187. — Elementary Diagram of Connections of Boat Cranes. 



A view of a controller used with boat cranes is shown in Fig. 188. 

The brake is of the disc type 
and is contained in a cast-steel 
frame, arranged to be bolted to 
the same foundation as the 
motor. Within the frame and 
surrounding the extension of 
the armature shaft, a series of 
discs are arranged, alternate 
discs being keyed to the shaft 
and the intervening discs being 
keyed to the frame. Several 
spiral springs serve to press 
the discs together and produce 
a powerful braking effect upon 
the armature shaft through 
the friction between the revolv- 
ing and stationary discs. A 
solenoid coil is provided which 
opposes the action of the 
springs, compressing them 
when the current is on and 
thus releasing the brake when 
the current fails from any cause whatever 




Fig. 



188.— R-62 Controller Used on 
Boat Cranes. 



414 Naval Electricians' Text Book 

Mechanical Connections. — For hoisting, a pinion on the hoisting 
motor armature shaft meshes with a gear wheel on a worm shaft, 
the worm wheel being secured to the drum shaft, over which passes 
the wire cable for hoisting. 

For revolving, a pinion on the revolving motor armature shaft 
meshes with a gear wheel on a worm shaft. The worm wheel with 
which this engages is secured to a vertical shaft and on the bottom 
of this a pinion is secured which meshes with a circular stationary 
rack. 

Automatic Brake. — In the addition to the magnetic disc brake 
with which the hoisting motor is held, there is generally fitted an 
automatic mechanical brake. 

The automatic brake is fitted on the worm shaft from which the 
hoisting drum is operated, and it in turn is operated through a gear 
wheel by a pinion on the armature shaft of the hoisting motor. 
On this worm shaft there is keyed a bushing in the shape of a 
sleeve with a flange on the end toward the worm. This sleeve is 
threaded on its outer circumference on the side away from the worm. 
A bushed ratchet wheel fits around this sleeve and against the side 
of the flange away from the worm. A fiber disc washer is inserted 
between the ratchet wheel and the flange of the bushing. There 
are two pawls secured to the framing of the crane entirely inde- 
pendent of the hoisting gear, set to engage the ratchet teeth alter- 
nately. A second fiber washer is fitted on the outboard side of the 
ratchet wheel. 

The gear wheel which is driven by the motor pinion is threaded 
to work on the screw on the outer surface of the bushing above 
mentioned. It is thus seen that the ratchet wheel works between 
the flange of this bushing and the face of the gear wheel which is 
towards the worm. 

A clutch which can be laterally adjusted by means of two locking 
nuts is keyed on to the end of the worm shaft. 

The operation of this brake is as follows : 

Hoisting. — In hoisting, the gear wheel is driven by the motor 
pinion and chases along the threaded bushing until it comes up 
tight against the fiber washers, the ratchet wheel and the flange on 
the end of the bushing. These finally become squeezed up tight 



Application of Motors 415 

and all run together thus operating the worm shaft and hoisting 
the load. In this direction the ratchet pawls are not operative, 
sliding over the teeth of the ratchet wheel. 

Lowering. — In lowering, as soon as the pinion of the armature 
shaft starts to drive the gear wheel, the ratchet pawls hold the 
ratchet wheel and the gear unscrews along the bushing, releasing 
the friction between the gear, the ratchet wheel and the flange of 
the bushing. If the load is then not sufficient to overhaul (and 
with the worm gear it will always be necessary to start the load in 
the lowering direction), the gear wheel unscrews until it comes 
against the clutch on the end of the shaft, which makes a positive 
connection and starts the load in the lowering direction. If, in 
lowering, the speed of the worm shaft becomes greater than the 
speed of the gear wheel, due to the load tending to overhaul the 
motor, this gear again screws along the bushing until it brings up 
against the fiber washers and the now fixed ratchet wheel. The 
friction between this ratchet wheel, the gear and the flange of the 
bushing checks the speed of the worm shaft until such time as the 
speed of the worm shaft has been reduced below the speed of the 
gear wheel, when the gear again unscrews itself and releases the 
friction. This setting up and unscrewing on the friction discs by 
the gear wheel will continue if the load overhauls the motor. But 
if this is not the case, and the motor keeps ahead of the load, the 
lowering is done by the motor which is driven from the gear and the 
clutch on the end of the shaft. 

Deck Winches. 

These are used on the upper and uncovered decks, forecastle and 
quarterdeck for general deck use, hoisting boats, hoisting on board 
stores, ammunition, etc., and in general use for connection with 
booms for coaling ship. They must of necessity be entirely water 
and dust tight and both electrically and mechanically strong. 

The electrical equipment consists of a compound motor, an R 
controller, pressed-ribbon rheostat, MQ circuit breaker and a re- 
versing cylinder. 

The electrical connections are shown in Fig. 189 where the func- 
tion of the controller is readily seen. For reversing, there is a 



416 



Naval Electricians' Text Book 



separate cylindrical switch, shown on the right, which reverses the 
armature current while allowing the field current to remain in the 
same direction. 

The controller simply makes connection between the mains and 
the armature and field, and controls the starting resistance. Ee- 
versal is accomplished by turning the reversing cylinder which 
reverses the direction of the armature current. 



CIRCUIT BREAKER 




Pig. 189. — Deck Winch Electrical Connections. Gen. Elec. Co. 



An interior view of the controller is shown in Fig. 190. 

Mechanical Connections. — The motor is mounted on the founda- 
tion of the winch and is connected to the driving shaft by gear 
wheels, one on the armature shaft and the other on the driving 
shaft. The driving shaft has a drum at each end, and the shaft 
is fitted with a clutch by which one of the drums may be thrown out. 

A band brake is fitted on the armature shaft, the band lined 
with wood encloses the wheel and is set by the foot of the operator. 



Application of Motors 



417 




w^ 



418 Naval Electricians' Text Book 

Ventilation Equipment. 

The ventilation system installed on vessels of the navy may be 
generally divided into two classes, portable and fixed. ■ 




Enclosed Motor and Fan. 



Portable ventilating fans include those of J horsepower for use 
in ventilating closed spaces that may be occasionally used, princi- 



Application of Motors 



419 




Fig. 192. — Open Motor and Fan. 



420 



Naval Electeicians' Text Book 



pally the double bottoms and holds and for this purpose are fitted 
with flexible tubing to the delivery side. They also include the 
•J and -^ horsepower fans for ventilation in state-rooms and small 
isolated store-rooms, and are generally of the bracket and pedestal 
type. 

For the fixed ventilation units, different combinations of fans 
and motors have been installed, the fans being made by B. F. 
Sturtevant & Co. and General Electric Company, and motors by 
The Sturtevant Company, Holtzer-Cabot Company, and General 
Electric Company. 








rSESJLsf j 



- M 




Fig. 193. — Controlling Panel for Ventilating Blowers. 



The fans generally are of the monogram or steel-plate type, the 
former being used for fans requiring small power. The steel-plate 
fans are designated in size by their diameter. They are built up of 
steel plate and angle bar and the fan wheels are of steel with 
brass hubs. 

The motors are either enclosed or open, depending on their loca- 
tion and all are directly connected to the fan shafts. 

Views of ventilating units furnished by the General Electric 
Company, showing enclosed and open motors directly connected to 
the fans are shown in Figs. 191 and 192. 



Application of Motors 



421 



Controlling Panels for Ventilating Sets. 

A general type of controlling panel is similar to that used for 
chain-ammunition hoists, but for those requiring a varying speed, 
obtained by changing the resistance of the field circuit a form 
shown in Fig. 14:4: is used. 

This latter requirement is also met by a form of controlling 
panel, shown diagrammaticalry in Fig. 193. 

Electrical Connections of Desk and Bracket Fans. — These small 
motors of -J and -^ horsepower are series wound and fitted with 
three speed contacts, effected by varying the resistance in series 
with the armature and field. 




Fig. 194. — Connections of Desk Fans. 



The connections of the controlling and starting switch with the 
rheostat is shown in Fig. 194. 

The connection board B is of porcelain mounted in the base of 
the bracket or stand. A is the starting arm, moving over the con- 
tact pieces shown, which are connected to different portions of the 
rheostat, or starting resistance R. On the first contact as shown, 
the circuit is open, and on moving A to the right on the first con- 
tact, the circuit is established from the supply main to the motor 
field, then through the armature, back to the pivot contact of A, 
then through all of the resistance R, back to the other main. On 
the second contact, more resistance is cut out and on the last con- 
tact R is short-circuited when the motor is running at full speed. 



422 Naval Electricians' Text Book 

Water-Tight Door and Hatch Equipment. 

The present practice of operating water-tight doors and hatches 
is through the agency of electric motors, and each hatch or door is 
operated by its own separate motor. The power is conveyed from 
each motor through gearing to the door or hatch ; for vertical doors 
a worm engages directly with a worm rack on the door, and for 
horizontal doors, a worm engages a worm wheel actuating a shaft 
carrying pinions which engage with racks on the doors. 

The motor with its controller is mounted in a power box, and in 
addition to the connections to each motor, there is an auxiliary 
circuit leading to an emergency station or stations, in the chart- 
house, or on the bridge, which controls a device for showing auto- 
matically whether the door is open or shut. The emergency station 
is fitted with a switch by which current is sent through all the 
operating motors, so that the doors or hatches may be closed almost 
simultaneously, current being on four or five motors at a time. 

The controller is a somewhat complicated affair and has three 
separate functions : ( 1 ) to allow each door or hatch to be opened or 
closed by local working, (2) to allow each to be operated practically 
at the same time from the emergency station, (3) to allow each or 
any door or hatch to be operated locally when closed from the 
emergency station.. In the last operation, a door or hatch that has 
been closed from the emergency station may be opened locally, but 
it will immediately close automatically if the emergency switch is 
closed. When each door or hatch is completely closed or meets 
with an unyielding resistance, a limit switch in the controller acts 
to cut off the current to the motor for closing, but leaves current on 
for operating the door for opening. 

Wiring Diagram. — The general scheme of wiring is shown in 
Fig. 195. 

L ± and L 2 are power mains with connections to the main switch- 
board or distribution boards. The motors M are compound wound, 
bipolar and iron-clad type, controlled each by its controller marked 
C. The emergency switch is marked E, and when this is turned 
in the direction of the arrow, circuit is completed through the right- 
hand positive connection from the power mains to and through the 



Application of Motors 



423 



switch, through the solenoids, S, and to the negative main. The 
energizing of the solenoid* attracts the core which closes the 
emergency switch in the controller when current is sent through 
each motor by its connection to the power mains. When each 
motor has closed its own door, the motor can still be controlled for 
opening by operating the local switch at the controller, but on 
releasing it, the motor will immediately operate to close the door 
as long as the emergency switch is closed. 

As each door is closed, circuit is made by means of the auxiliary 
contacts, A, through a lamp, L, at the emergency station which 




Fig. 195. — Wiring Diagram of Motors. 



illuminates a dial showing the number of the door. After the 
emergency switch has been turned, the operator can press the push 
button P and can tell at a glance which doors are not closed. 
These lamps are also lit when each door is locally closed and the 
button P is closed. This button is normally kept open, but to tell 
what doors in the ship are open or shut, it is only necessary to close 
the contact P. 

In order to make sure that current is on, there is a tell-tale red 
lamp, marked RL and so connected that as soon as current goes 
through the first solenoid, the lamp will glow and will continue to 
burn until the emergency switch is turned to the off position. 



424 



Naval Electricians' Text Book 



Miscellaneous Electric Equipments. 

In addition to the general electric equipments described in the 
preceding pages, there are many examples of individual machines 
and tools driven by electric motors. In all such cases, as machine- 
shop tools, laundry machines, and 
such individual electric-driven 
machines as dishwashers, potato 
peelers, dough mixers, ice-cream 
freezers, printing presses, pumps, 
air compressors, etc., the power 
required is small, and the equip- 
ment usually consists of the mo- 
tor, either directly connected to 
the machine, or through gearing 
or belting, and a starting panel of 
the general characteristics already 
described. With the help of pre- 
viously described equipments, 
these individual electric equip- 
ments should present no difficul- 
ties either in principle or in op- 
eration. Although the controllers 
and starting panels may be of dif- 
ferent construction, their opera- 
tion should be readily understood. 
A general form of controlling 
panels for use with motors of less 
than 3 horsepower is shown in 
Fig. 196. 




Fig. 196.— Type C. R. Controlling 
Panel. Gen. Elec. Co. 



CHAPTER XIX. 

PRINCIPLES OF ALTERNATING CURRENTS. 

All electric generators induce alternating currents in their arma- 
ture windings, due to the conductors passing alternately magnetic 
poles of opposite polarity; in which operation the E. M. F. induced 
by the cutting of the lines of force, is reversed as the conductor 
passes from pole to pole. One of the chief differences between 
continuous and alternating current generators is in the method of 




Fig. 197. — Coil in Magnetic Field. 



collecting the current from the armature conductors ; the continuous 
current generator requiring a commutator to rectify the alternating 
currents of the armature conductors into current in one direction 
in the external circuit, while in an alternator the currents are col- 
lected by rings and the currents in the external circuit are in the 
same direction as those in the armature conductors. 

Variation of E. M. F. — A reference to Fig. 197 will show a 
rectangular coil ABCD at right angles to the magnetic field be- 
tween the poles A 7 and S. 

The E. M. F. generated by a coil moving in a magnetic field is 
numerically equal to the rate at which it cuts the lines of force. 
The rate of cutting varies with the position of the coil as it moves 
around its center of revolution 0. It must be remembered that 



426 



Naval Electricians' Text Book 



the active cutting portions of the coil are AC and BD, the remain- 
ing portions CD and AB simply completing the closed circuit. 

In the position of the coil shown by AB, the rate of cutting of 
lines of force is least, as at that position, the motion of the con- 
ductor AC is parallel to the lines of force, but in a position 90° 
from AB, as at EF, the rate of cutting is greatest, as at this posi- 
tion, the motion of the conductor is perpendicular to the lines of 
force. 

If V represents the velocity of the coil in its revolution, the 
velocity at any instant is the linear velocity in a tangent to the 
circle of revolution at that point. In Fig. 197 the velocity at the 
point E is represented by the velocity in the 
tangent at that point, V, shown in Fig. 198. 
As the generated E. M. F. is greatest at that 
point, the maximum E. M. F. may also be 
represented by V, for the E. M. F. is numeric- 
ally equal to the velocity, or rate of cutting. 
The rate of cutting at any point is propor- 
tional to the component of V that is perpen- 
dicular to the lines of force, that is, the ver- 
tical component, and at any point H, the 
vertical component is V cos 0', or V sin 0, 
where 6 is the angle turned through from the 
initial or zero position, and therefore, the E. M. F, at any point is 
equal to V sin 6, where V is the maximum E. M. F. 

A curve of variation of E. M. F. is shown in Fig. 199, where for 
each value of $ measured horizontally in degrees from 0°, ordinates 
are set up vertically to represent V sin 6, the E. M. F. for that 
position of the conductor, and a curve drawn through the points so 
obtained. 

This is a sine curve and the change of direction of the E. M. F. 
which occurs when the conductor begins to cut the lines in the 
reverse direction is shown by the curve crossing the zero line. 
E. M. F's. above the line are called positive and those below 
negative. 

Definitions. — The time taken by the E. M. F. to pass through a 
complete series of changes such as represented in Fig. 199 is called 
a period, and the complete operation is called a cycle. 




Fig. 198. 



Principles of Alternating Currents 



427 



The frequency is the number of periods, or number of cycles 
per second. 

The amplitude is the maximum value of the variable E. M. F. 

The phase of any point is measured by the angle swept over by 
the point from the zero position. Thus the phase at position of 
maximum positive E. M. F. is 90 ° , maximum negative E. M. F. 
is 270°, at minimum E. M. F. it is 0°, 180° or 360°. The phase 
may also be measured in terms of a complete cycle, thus the phase 
at 90° is i, at 180° is \, at 360° is 1, etc. 




Fig. 199.— Curve of E. M. F. 

Example. 

A bipolar alternator gives a maximum of 500 volts with a frequency 
of 100, what will be the phase and voltage 3y 3 seconds after starting 
from the point of minimum E. M. F.? 

In 3% seconds, a coil will have passed through 3y 3 x 100 x 360 
degrees, or 333 complete cycles and y 3 of a cycle, and the coil will be 
in phase 360° -h 3 = 120°. 

The value of the E. M. F. at phase 120° will be V sintf or 500 X sin 
120° = 433 volts. 



Effect of Increase in Number of Poles and Conductors. — The 

frequency of the alternations depends upon both the speed with 
which the conductors are moved and upon the number of the alter- 
nate poles under which the alternations take place. In the case of 



428 Naval Electricians' Text Book 

a multipolar machine a period will be the time occupied for a con- 
ductor to move from one pole to a similar position under the nearest 
pole of the same polarity. In a 10-pole alternator there will be five 
periods per revolution, or the frequency per revolution will be 
five. In general, if 

n = number of revolutions per second, 

P = number of pairs of poles, 

n' = frequency. 

Then '_*L X Z 

n — 60 " 

In order to increase the E. M. F. generated in a machine, the 
number of conductors must be increased, and the total E. M. F. 
generated in an armature composed of a great number of conductors 
will be equal to the sum of the voltages in the individual con- 
ductors if (1) the conductors under opposite poles are joined alter- 
nately at the front and bach of the armature so that the E. M. F. 
induced in the successive conductors in opposite directions is made 
to act in the same sequence in the complete ivinding, and (2) if the 
conductors passing under a pole at any time are sufficiently close 
together to enter and leave the pole at nearly the same time. 

Self-induction in an Alternating Current. 

An alternating current is always accompanied by a changing 
magnetic field, the rapidity of the change being dependent on the 
number of the alternations. This rapidly changing field reacts 
on the current producing it, and has the same effect as though the 
conductor were moved through a field of as many lines of force as 
are produced by the current. The effect of the changing field on 
the conductor is to generate an E. M. F. called the E. M. F. of self- 
induction, which acts to oppose any change in the current. If the 
current is increasing, this self-induction tends to oppose the in- 
crease and if decreasing, it opposes the decrease. 

This E. M. F. of self-induction, sometimes called lack or counter 
E. M. F. is dependent on the rate at which the magnetic field due 
to the current changes, and hence is proportional to the rate at 
which the current itself changes and not directly on the current or 
on the number of lines of force. 



Principles of Alternating Currents 



429 



Curves of Current and Rate of Change of Current. — Fig. 199 
shows that the induced E. M. F. in an alternating current and 
consequently the current produced thereby is proportional to the 
sine of the angle through which the conductor has moved, and 
consequently the rate of change of current is proportional to the 
differential of the sine or is equal to the cosine of the angle in 
radians. Fig. 200 shows curve I plotted as a current curve, and 
II, a rate of change of current curve. 



80 20 




Fig. 200. — Curves of Current and Rate of Change of Current. 



Curve I is plotted from the equation y = C sin x. Curve II 
is plotted from the rate of change of curve I. The rate of change 
of the sine of an angle is equal to its cosine when measured in 
radians. As there are 2tt radians in 360° or one cycle, the rate of 
change per cycle is 2-rr times the cosine of the angle. The equation 
for plotting curve II then becomes y' = 2-n-C cos x, and the ordi- 
nates are plotted as currents and the abscissae as angles. The 
maximum value of the rate of change of current occurs when 
x = 0°, for then y = 2-rrC and the maximum ordinate is 6.3 times 



430 Naval Electricians' Text Book 

the maximum value of C. In the example chosen, the maximum 
value of G is 12 amperes, and the maximum value of the rate of 
change of current is 6.3 X 12 = 75.6 amperes. For convenience 
in plotting, the scale of curve II is taken four times as great as 
curve I. 

It will be noticed that the minimum value of the rate of change 
of current occurs when x = 90°, for then y = 2-n- cos 90° = 0. 
The above considerations show that the curve of rate of change of 
current differs in phase by \ of a period from the current curve, 
and that it is in advance in phase by that amount. 

Curve 77 could be geometrically plotted as follows: From any 
point P on the current curve draw a tangent PB and from P lay 
off a horizontal distance PA equal to the length of J cycle and draw 
a vertical line from A till it meets the tangent at B, then the dis- 
tance AB is the ordinate on the rate of change of current curve 
for \ cycle ; and for a curve for a whole cycle, such as II, the ordi- 
nate would be a distance four times as great. This ordinate would 
be a point on curve II corresponding to the phase of the point P. 

If the current passes through n cycles per second, the maximum 
value of the rate of change per second is 2imC. 

The coefficient of self-induction is equal to the E. M. F. induced 
by a change of one ampere per second, and if 

E = E. M. F. of self-induction 
L = coefficient of self-induction 

we may write, when the current is changing at the rate of one 
ampere per second 

E — L. 

If the ordinates of curve II are multiplied by n, it would be a 
curve of 2irnC, and if the current changes at the rate of %irnG 
amperes per second, the induced E. M. F. of self-induction is 

E — 27rnCL. (a) 

From a consideration of the above it is shown that when an 
alternating current is flowing, it gives rise to a back E. M. F. 
opposing the change of current, and to overcome this back E. M. F. 
an additional E. M. F. determined by equation (a) must be applied. 



Principles of Alternating Currents 431 

However, from the fact that the two curves of E. M. F. differ in 
phase, not all of the E found from equation (a) is necessary, but 
it offers a means of determining what the real applied E. M. F. 
must be in order to produce a certain current. 

Curve of Applied E. M. F. 

Suppose it is required to find the applied E. M. F. necessary to 
maintain a maximum current of 10 amperes in a resistance of 1.5 
ohms in a circuit with a self-induction of .005 henry. The alter- 
nator has 12 poles with a speed of 1200 revolutions per minute. 

There are now two E. M. F's. to be considered : first, that neces- 
sary to supply 10 amperes in a resistance of 1.5 ohms, which is the 
same E. M. F. that would be required in a continuous current ; and, 
second, that necessary to overcome the back E. M. F. due to self- 
induction. The current curve as plotted is marked C in Fig. 201. 

The resistance E. M. F., as it is called, can be plotted to any 
convenient scale, by multiplying the values of the current at any 
instant by the resistance of the circuit. Thus the maximum value 
of the resistance E. M. F. is, for the example cited, 10 X 1-5 = 15 
volts. This is shown plotted as a curve of sines in Fig. 201, 
marked E x . 

The curve due to the change of current, or, what is the same 

thing, the curve of back or inductance E. M. F. can now be plotted 

on the same scale, from the equation E = 2irnLC, remembering 

that the curve of resistance E. M. F. is J period in advance of the 

curve of back E. M. F. 

12 1200 
The frequency is -^ x gr> =120, and the maximum value of 
Z bO 

E is 2tt X 120 X -005 X 10 = 38.8 volts. 

The alternator must supply a voltage equivalent to both of the 
E. M. F ? s. if the condition required is to be maintained, and at 
any instant, the applied E. M. F. must be equal to the sum of the 
resistance and inductance E. M. F's. at that instant. Curve E 3 is 
plotted by adding together algebraically the ordinates of the two 
curves E x and E 2 . In the example, the greater portion of the 
applied E. M. F. is needed to overcome the inductance, but where 
the inductance is small, the greater part might be necessary to over- 
come the resistance. 



432 



Naval Electricians' Text Book 



It is seen that the required E. M. F. is not the arithmetical sum 
of the two E. M. Fs. arising from the fact that the two E. M. Fs. 
are not in the same phase. 




Fig. 201.— Curves of E. M. F. and Resultant E. M. F. 



Angle of Lag and Lead. — It will be noted that the curves E s 
and C are not in phase with one another, the difference in phase 
being measured on the horizontal scale between the points at which 
they pass through their zero values. If the current curve passes 
through its zero value at an angle greater than the total E. M. F. 
curve does, the current is said to lag by an amount equal to the 



Principles of Alternating Currents 433 

angle of lag, and if the opposite is the ease, the current is said to 
lead by an amount equal to the angle of lead. Inductance always 
causes an angle of lag which depends on the nature of the resist- 
ances and other apparatus in circuit. 

Graphic Representation of Alternating Currents. 

The two curves, C and E 3 , in Fig. 201, show the changes under- 
gone by the applied E. M. F. and resulting current in one cycle, 
or in one alternation, and for any given value of E. M. F. the result- 
ing current can be found. From the fact that the two curves differ 
in phase, the maximum current does not occur at the same time as 
the maximum E. M. F. To find the current corresponding to maxi- 
mum E. M. F. it is only necessary to draw an ordinate through the 
position of maximum E. M. F. and the portion of this ordinate 
common to the current curve will be the desired value. Thus, in 
Fig. 201, the desired current is about 5.5 amperes. 

Although the varying E. M. F's. and currents can be well repre- 
sented by curves, such as shown in Fig. 201, yet the process of plot- 
ting is tedious, and another method of plotting by right lines, 
called vector diagrams, and which will show all the varying quanti- 
ties, has been devised. 

As the resistance E. M. F. and inductance E. M. F. differ in 
phase by J of a period, or are 90° apart, they may be represented 
by straight lines at right angles to each other, the lines by their 
length representing the values of the E. M. F's. If the triangle 
is completed by drawing the hypothenuse, this will represent by its 
length the value of the resultant E. M. F. These values will give 
the maximum value of these quantities. To show the varying 
values of these quantities it is only necessary to project their 
lengths on a straight line suitably placed. Such an arrangement 
is shown in Fig. 202. 

From O is drawn to scale OE x in any direction, the maximum 
value of the inductance E. M. F. and equal to lirnCL, and from E ± 
and at right angles to OE 1 is drawn E X E 2 , the maximum value of 
the resistance E. M. F. and equal to CR. Then the hypothenuse 
OE z is drawn and it will represent, according to the scale adopted, 
the maximum value of the resultant E. M. F., and equal to 
C\/£ 2 + (27rnL) 2 . 



434 



Naval Electricians' Text Book 



The instantaneous values of the E. M. F's. are found by project- 
ing E t E 2 E 3 on the horizontal line ON, where the distances OA, 
OB, BA measured to scale will be the instantaneous values at any 
instant when the whole triangle is revolved about 0. The instan- 
taneous value of the resultant E. M. F. is the sum of the instanta- 
neous values of the component E. M. F's. Thus the instantaneous 
value of E 1 is OA, of E 2 is AB (negative) and of E 3 is OB, which 
is the sum of OA -\- ( — AB) . As the triangle is revolved about 
0, the instantaneous values of the variable quantities may be ob- 
tained at any instant. When the line OE t is on the line ON, the 



E3.E, 




B A 

Fig. 202. — Component and Resultant E. M. F's. 



projection of E 2 is zero, and E ± is a maximum as previously seen in 
Fig. 201. 

The angle between the two vectors representing the curves E 2 
and E 3 is the phase, represented by <j> in the figure. 

Magnitude of Kesultant E. M. F. — In Fig. 202 it is shown 
how the resultant E. M. F. may be obtained when the component 
E. M. F's. are known, and as this is the hypothenuse of a right 
triangle, the value of the resultant E. M. F. can readily be 
calculated. 

OE 2 = OE 2 + E X E 2 , 
or V 2 = (2TrnCL) 2 + C 2 R 2 , 

and V — C\/R 2 + {^nL) 2 . 

Of this value V, CR is spent in overcoming the resistance of the 



Principles of Alternating Currents 



435 



circuit, and C'2irnL in overcoming the back E. M. F. of self-induc- 
tion. If there is no self-induction L = 0, when V = CR, in 
accordance with Ohm's law. 

Impedance. — It has been shown above that the current in an 
alternating circuit cannot be calculated by Ohm's law, owing to the 
effects of self-induction, and it acts as though the resistance instead 
of being R was increased to \/R 2 -f- (2ttwL) 2 . The current is not 
generally governed by the resistance but by the inductance. In 
Ohm's law, the voltage divided by current gives the resistance, but 
in alternating currents, the voltage divided by current gives a 
factor, represented by V^ 2 + (2ttwL) 2 , which is called the 
impedance. 




2arn L 
Fig. 203. — Triangle of Resistance and Impedance. 



Fig. 202 shows that each side of the triangle of E. M. F's. con- 
tains the current factor C, and if each side be divided by C, there 
will remain a triangle which can be plotted to a scale of resistance. 
These three sides are represented in Fig. 203. 
The side of the triangle BC = resistance = R, 

AC — impedance = y# 2 + (2rnrL) 2 , 
AB = reactance = 2-n-nL. 

If R is small, the impedance becomes practically the reactance 
and if the inductance is small, the impedance becomes nearly equal 
to the resistance. 

From a consideration of the factors entering into the formula 
representing the impedance, it is seen that it depends upon the 
ohmic resistance R, the inductance L, and the speed, or frequency, 
n. The resistance is independent of frequency, whereas the react- 
ance depends directly on the frequency. 



436 Naval Electricians' Text Book 

Capacity in an Alternating Circuit. 

All conductors possess a certain amount of capacity depending 
on their form and their nearness to other conductors. This 
capacity of insulated conductors is so small that it does not prevent 
the current flowing from obeying Ohm's law ; but if the circuit pos- 
sesses electrostatic capacity given by some form of condenser, a 
charging current will have to flow first into the condenser before 
the voltage acting on the resistance of the circuit can attain the 
full value of the applied E. M. F. 

In the case of an alternating current, there is a charging current 
at each reversal of E. M. F., and the total current is the sum of the 
charging current and the normal current following Ohm's law. As 
soon as a condenser is charged to full potential, the flow of current 
will cease until the voltage of the applied current changes. A 
condenser in a continuous current circuit thus stops all flow of 
current, but in an alternating current, the potential is continually 
changing, and the current flows into and out of the condenser, 
changing its sign. 

If Q = quantity of electricity in coulombs 
K = capacity of a condenser 
and E = difference of potential between terminals of the con- 
denser. 

Then Q = KE, and a conductor has unit capacity, one farad, when 
it is raised to unit voltage, one volt, by one coulomb of electricity. 

The current flowing into a condenser is equal to the rate of 
change of the charge. 

The current is the rate at which quantity of electricity flows, and 
the charging current will be the rate of change of quantity, or rate 
of change of KE, and will be equal to the current flowing into the 
condenser. This charging current, or the current flowing into the 
condenser, is 

# and since Q = KE, -2 = %E , or 
t to 

the charging current is equal to the capacity times the rate of 

change of voltage at the terminals. 

The relation between charging current and the applied voltage 



Principles of Alternating Currents 



437 



may be graphically shown as in the case of the current curve and 
the rate of change due to self-induction shown in Fig. 200. 

In Fig. 204, is plotted curve I for a maximum E. M. F. of 12 
volts, and its rate of change is shown in curve II. For convenience 
in plotting, this curve is plotted for one radian, and the maximum 
value for one cycle would be 2tt X 12 volts, and for a frequency of 
n per second, it would be 2irn X 12 volts. 

2(H 




Fig. 204. — Curves of E. M. F. and Charging Current. 



If the circuit had a capacity of 400 microfarads and a frequency 
of 100, the capacity factor would be 



o tz 2 X 3.14 X 100 X 400 
2-irnK, or q-nn ^ aaa =.25. 



Since -*- 



KE 



1,000,000 
, to find the ordinate of the charging current, 



E 



each ordinate of -r , the rate of change of E. M. F., or curve II, 
z 

must be multiplied by .25. The maximum value is .25 X 12 = 3 
amperes, which is plotted as curve III on a second scale of amperes. 



438 Naval Electricians' Text Book 

An inspection of Fig. 204 shows that the charging current differs 
in phase from the E. M. F. and is always one-quarter of a period in 
advance, and the effect of introducing capacity in an alternating 
current is to cause the current to lead, being just opposite to the 
effect caused by induction. In addition to this charging current, 
which is out of phase with the E. M. F., there is the current due 
to the resistance of the circuit and which is in phase with the 
E. M. F. This curve of current could be plotted on the same 
diagram by dividing the ordinates of the voltage curve by the 
resistance, and the total resulting current curve could then be found 
by adding algebraically the ordinates of the charging and resist- 
ance currents, exactly as in the case of rinding the resultant curve 
of E. M. F. in Fig. 201. 




Vector Diagram of Currents. 



Vector Diagrams. — Similar to the case of resultant E. M. F. 
the resultant current may be found by vectors, one drawn to scale 
to represent the resistance current, and another at right angles to 
represent the charging current, when the hypothenuse will repre- 
sent the resultant current according to the scale adopted. The 
resistance current is in phase with the E. M. F. and the angle be- 
tween this vector and the resultant current vector will be the angle 
of lead. Such a drawing is represented in Fig. 205. 

Impedance Due to Capacity. — The impedance, as shown under 
induction, is equal to the E. M. F. divided by the current, and 
therefore the resistances of the vectors in Fig. 205 may be obtained 
by dividing the E. M. F. by the respective currents. Thus, for 
AB, the resistance is 

and for BC, the resistance is 

1 
E -^ 27rnKE = 



2irnK 



Principles of Alternating Currents 



439 



A similar diagram may now be drawn for the resistances as in 
Pig. 206, from which the impedance may be found. 



\Z R2 +{^xJ 



The impedance is V AC 2 = ^/ AB 2 + CB 2 = 

The current in an alternating circuit depends upon the resistance, 
and capacity in circuit and the frequency of the alternations. 

Impedance Due to Induction and Capacity. — Since induction 
produces lag and capacity, lead, when these two are connected in 
series, their effects are opposed and the combined effect of the 
impedance is given by the formula 



^ 



R' 



2-nL 



i V 

and the expression for the resultant current is 

E 



° = V*H^ l -2^rI 




Fig. 206. — Resistance Diagram. 



Power. 

The power of an alternating circuit, like that of a continuous 
current, is the product of the E. M. F. and current. This is true 
for any part of the circuit under consideration, and for any part 
of an alternating circuit, the power developed is numerically equal 
to the product of the current flowing in the portion considered and 
the difference of potential between the two points of the circuit. 
In the case of alternating currents, as the current and E. M. P. are 
not in phase, they may be acting in opposite directions, in which 
case their product must be considered negative. 



440 



Xaval Electricians' Text Book 



When the power is negative the circuit is not receiving power 
from the source of supply, but is giving back power to assist in 
driving the generator of the currents. As energy is equal to power 
times time, the energy actually given to any external circuit is equal 
to the arithmetical sum of the power of the circuit multiplied by 
the time. 

550 50 



440 40 



110 



| i" | !_! 


45° 9,0° 135NL__^T80 C 225° 270° 3 ^v§T 


J 



Fig. 207. — E. M. P. Current and Power Curves. 



The average power given to an external circuit is the average 
value of the product of volts and amperes. The effect of negative 
power is shown in Fig. 207 where are plotted curves of E. M. F. 
and current, from which is plotted a third curve, the watt curve, 
from values found by the product of volts and amperes for the 
same instant. Curve I represents the resultant current due to 
a resultant E. M. F. shown in curve II, the current leading the 



Principles of Alternating Currents 441 

voltage by a phase of 45°. If for any instant, the product of the 
instantaneous values of E. M. F. and current be found, it will give 
the power developed in the point of the circuit under consideration. 
If a number of points be so determined for a cycle, a curve drawn 
through these points will represent the power or watt curve, and 
curve III has been so determined. It must be remembered that all 
points above the horizontal zero line are to be reckoned as positive 
and those below as negative, and the product of two positive quanti- 
ties or two negative quantities will be positive, while the product of 
a positive and negative quantity will be negative. Thus, all the pro- 
ducts will be positive except between 135° and 180°, and between 
315° and 360° which will be negative. The curve is roughly plotted 
to the scale of watts shown on the left-hand side of the diagram. 

The average power developed in the circuit is the average value 
of the product of volts times amperes in the circuit. This is found 
by adding together ordinates of the watt curve and dividing by 
the number taken. Ordinates below the zero line must be sub- 
tracted from those above. The average power is shown in the 
figure by the dotted line AB. 

This average power is that indicated by a wattmeter. The read- 
ings of a voltmeter and ammeter connected in circuit will not give 
the true average power by taking their product, for their readings 
are given independent of the phase of the voltage and current. 
If these are in phase the product of the volts and amperes as shown 
by the instruments should be the same as that indicated by a watt- 
meter, but not otherwise. 

If the current and voltage were in phase, there would be no 
negative power and the average power would be greater, but as the 
phase difference increases up to 90°, the negative power increases 
and the positive decreases, and at 90° they would be equal, or the 
average power given to the circuit would be zero, or the current 
would be wattless. A wattmeter under such condition would indi- 
cate zero, while the voltmeter and ammeter would indicate as 
though the phase was zero, as they would under all conditions of 
phase. 

The product of the voltmeter and ammeter readings gives the 
apparent watts. 



442 Naval Electricians' Text Book 

The power factor is the ratio of the true watts to the apparent 

watts, or 

, , true watts 

power iactor = — ,, . . 

r volts X amperes 

or true power == volts X amperes X power factor. 

The resultant E. M. F. consists of two components, one in phase 
with the current and one differing in phase by one-quarter of a 
period. When the resultant E. M. F. differs in phase from the 
current, by one-quarter of a period, the average power is zero. 
One component of the E. M. F. therefore does not affect the power 
of the circuit, and is called the idle E. M. F. while the other com- 
ponent multiplied by the current gives the total power, and this 
component is called the energy E. M. F. 

The components, energy and idle E. M. F's. ar^e at right angles 
to each other, the hypothenuse being the total E. M. F., and the 
phase is the angle between the energy E. M. F. and total E. M. F. 

If E is the total E. M. F. the power given out is C X energy 
E. M. F. = C X E cos <f>, where <f> is the phase. 

As the power given out = C X E X power factor, it follows that 
the power factor is equal to the cosine of the angle of phase. 

Comparison of Values of Direct and Alternating Currents. 

In order to compare direct and alternating currents, it is neces- 
sary to compare effects which are independent of the direction of 
the current, and such a comparison is found in their heating effects 
when passed through resistances. 

A direct current of C amperes flowing through a resistance B 

will develop C 2 R joules per second, and an alternating current of 

equivalent value will also develop the same number of joules per 

second in the same resistance. Hence the average value of C 2 

alternating must equal the average value of C 2 direct. The average 

value of the square root of C 2 direct is C, but the average value of 

the square root of C 2 alternating is not the same as the average 

value of C alternating. 

2 
The average value of the ordinates of the sine curve is— = .635, 



Principles of Alternating Currents 443 

but the square root of the squares of the ordinates = .707 of the 
maximum height, or— retimes the maximum value. 

The average value of an alternating current is not used, but 
rather the alternating current which is equivalent to a direct cur- 
rent. This last is called the virtual current and is equal to the 
square root of the average value of the squares, and it is this value 
which is registered on an ammeter and the one used in designating 
the strength of an alternating current. 

The same remarks apply to an alternating E. M. F. and the 
virtual volts are those shown on a voltmeter. If a voltmeter 
showed 70.7 volts, the maximum voltage would be 100 volts and an 
ammeter that showed 100 amperes would be varying between and 
141 amperes. 

Most voltmeters and ammeters for measuring alternating cur- 
rents give readings proportional to the mean values of the square 
of current or voltage, and if they are designed so that the deflection 
is proportional to the deflecting force, the division of the scale 
marks are uneven, as the distance between marks increases in the 
ratio of the square of the value being measured. 

Average Power. — The average value of C 2 R in an alternating 
circuit is one-half the maximum value. The maximum value of 
the power is equal to the product of maximum volts and maximum 
amperes, and the average power is J (maximum volts times maxi- 
mum amperes) or—— maximum volts times —= maximum amperes. 
\/2 v2 

These last factors are the virtual values, or 

average power = virtual volts times virtual amperes. 
It is the average value of the watts which gives the true power 
in a circuit, and this can be found by taking the product of the 
virtual volts and virtual amperes as shown by the instruments, 
if the E. M. F. and current are in phase. If not in phase, the 
average value of the power is -J CE cos <J> 9 where C and E are virtual 
values and <f> the angle of phase. 



CHAPTEE XX. 
DYNAMO ELECTRIC MACHINES. 

A d} T namo electric machine is defined to be one for converting 
energy in the form of mechanical power into energy in the form of 
electric currents or vice versa by magneto-electric induction, the 
operation being in general that of setting conductors to rotate in a 
magnetic field. 

So far the dynamo electric machines considered have been the 
generator and the motor, one furnishing and the other absorbing 
continuous currents. Besides these machines considered as simple 
units, there are others built from combinations of these two, with 
combinations of alternating and continuous E. M. F. and currents, 
each designed to satisfy some definite requirement. 

Motor Generators. 

These machines are generally designed to change from a con- 
tinuous current at one voltage to a continuous current at another 
voltage, and are sometimes called continuous current transformers. 
To do this it is necessary to employ a rotating apparatus which is a 
combination of a motor and a generator. Two complete machines 
may be used, each with its own armature and own commutator, 
fixed to a common shaft, or one single armature may be wound 
with two separate windings connected to separate commutators. 
In the first case, there would be two separate magnetic fields and in 
the second there would be but one. 

Current is supplied to one set of windings through its proper 
commutator at a certain voltage, and the field being excited this 
machine will act as a motor and will drive the other set of windings 
as a generator, generating an E. M. F. at its brushes, whose value 
depends upon the number of windings, the speed and the strength 
of the field. 

If the speed and field are the same, the E. M. F. developed in 



E-JJ^a — E 2 C 2 a Or -jT~ — fC, 

^ 1 = ©_C ia r = e-^p, (3) 



Dynamo Electric Machines 445 

each winding is proportional to the number of turns of wire in the 
winding. 

Using the notation of Chapter XII, the relation between the 
various E. M. F's. and currents are given in the equations : 

For motor, 

(£ = E x + C ia r ia . (1) 

For generator, 

e = E 2 — C 2a r 2a . (2) 

The ratio of E ± to E 2 , the total E. M. F's. generated by each 
winding is constant, or 

E 2 ~ *> 
and so will also the ratio C ± to C 2 be constant, as 

or from (1) 

and from (2) 

E x = ek + C 2a r a lc, (4) 

and from (3) and (4) 

This gives an expression by which e, the difference of potential 
at the generator brushes can be found from ©, the difference of 
potential at the motor brushes. 

The amount of power developed by the generator depends on the 
efficiency of the system, which is the ratio of the input of the 
motor to the output of the generator, or using the previous notation 

Efficiency = — jj 

where C x represents the current absorbed by the motor and C 2 the 
current delivered by the generator. Thus a system with an efficiency 
of 80 per cent, absorbing 50 amperes at 125 volts would deliver the 
50 amperes at 100 volts, thus 

125 X 50 X 80 _ 
100 X 100 ~" DU ' 
or if the windings in the generator were only half as many it would 
deliver 100 amperes at 50 volts. 



446 Naval Electricians' Text Book 

Motor generators are used on ships of the navy in connection with 
the turret-turning and gun-elevating systems, the generators pro- 
ducing variable voltages, effected by varying the field excitation 
of the generator ends. 

The specifications for motor-generator sets for gun-elevating 
equipments as issued by the Navy Department are as follows : 

Specifications for Motor-Generating Sets for Gun-Elevating Equipments. 

1. To consist of a direct-current 120-volt motor and a direct-current 
130-voJt generator of such capacity as may be directed, with common 
annealed cast-steel frame having suitable supporting feet; both arma- 
tures to be mounted on a common shaft, with commutators toward the 
shaft ends; unless otherwise specified, rotation to be right hand — i. e., 
clockwise, facing motor end; bearings to be supported by end shields,; 
these shields to be secured by bronze bolts, and so designed that weight 
of armature is taken by a flange forming a finished working fit in end 
of frame. Sets to be convertible to wall or ceiling suspension merely 
by rotating the end shields. 

2. Sets to be of the totally enclosed and water-tight type, with suit- 
able hand-holes for inspection and adjustment of brush rigging and for 
inspection of commutators; all holes to be fitted with water-tight 
covers, setting up on either %-inch cloth insertion gaskets of navy 
standard quality (Spec. 23P4) or on strip gum gaskets; these covers 
to be satisfactorily secured by tobin bronze bolts with hinged com- 
position handles to permit their ready removal and replacement without 
the use of tools; each cover to have at least two securing bolts and a 
handle for lifting. Drain cocks shall be fitted to the frame to permit 
drawing off water which may collect on the interior. 

A slotted brass ^-inch pipe plug to be fitted from exterior to each 
end shield in proper position to permit by its removal inspection of oil 
rings and filling of wells; plug to be secured by swivel and about six 
inches of plumber's brass chain No. 2. 

3. Frame to enclose two separate magnetic circuits, each having four 
or more equally energized poles. 

4. Shaft to be of steel, with accurately fitted journals; to run in two 
bronze self-oiling bearings, one at each end of the frame; to be pro- 
vided with suitable means to prevent oil from bearings working along 
to armatures; bearings to be provided with sight glasses on oil cham- 
bers and suitable drains for removal of oil at will. 

5. Frame to be divided horizontally, the two parts to be bolted 
together, to permit ready removal of armatures and field coils. 

6. There shall be but two studs for the generator brush rigging and 
but two studs for the motor brush rigging, all to be accessible from the 



Dynamo Electric Machines 447 

top; the design of brush mechanism to be such that when end shields 
are rotated for wall or ceiling suspension the brushes will be main- 
tained in proper position relative to hand-holes. 

7. Generator field to be shunt wound to adapt the machine for 
furnishing power for the Ward-Leonard system of control. The satu- 
ration curve must show practically a straight line up to 110 volts 
(armature terminals) and must not show saturation at 140 volts. 

8. Sets to be designed for speed not exceeding 2000 revolutions per 
minute — the design to be with a view to minimizing weight and overall 
dimensions; speed variation between no load and full load and from 
full load to no load not to exceed 10 per cent of normal. 

9. Commutator bars or segments to be supplied on a shell which 
must be directly attached to the spider or keyed to the shaft; bars to 
be hard drawn copper, finished accurately to gauge; insulation between 
bars to be of carefully selected mica, gauged to uniform thickness and 
of such hardness as will wear evenly with the commutator bars. 

10. Bars to line with the shaft and run true; to be securely clamped 
by means of bolts and clamping rings; clamping adjustments to be 
accessible in finished armature. There shall be no openings by which 
any foreign substance can get to the interior of the commutators. The 
commutators and brush rigging must be designed to permit handling 
heavy and fluctuating loads up to as high as 200 per cent overload. 

11. Brushes to be of carbon; current density at normal full load 
not to exceed 35 amperes per square inch; each stud to carry two 
brushes; each brush on a stud to be capable of separate removal or 
adjustment, and means shall be provided for simultaneously shifting 
all brushes; brush holders to be of the sliding shunt-socket type; 
springs to be of material other than steel and must not be relied upon 
to carry the current; brush stud insulation to be absolutely moisture 
proof. 

12. Finished armatures to run true and be balanced both electrically 
and mechanically. The completed sets must run at all loads without 
noise or vibration. 

13. A name plate to be fitted to each motor generator in a con- 
spicuous place, containing the following data: , 

MADE FOR 

Bureau of Equipment 

by 

(Name of maker here.) 

Req. No. — . Date — . Rating — . 

Factory No. — . Volts. — . Amp. — . 

Field (Gen.) — . Amp. — . Ohms — . 

Factory number to be also stamped on the frame under the name 

plate. 



448 Naval Electricians' Text Book 

14. Separate name plates shall be fitted to indicate which is the 
motor and which is the generator end. 

15. The entire construction of the sets must be free from iron cast- 
ings as far as possible. 

16. The overall dimensions must not exceed the following: 8 kilo- 
watts, 21 by 21 by 40 inches long; 5% kilowatts, 19 by 19 by 32 inches 
long; Zy 2 kilowatts, 17 by 17 by 28 inches long. 

17. The design must be such that when installed in confined spaces, 
with but 4 inches clearance at each end, the end-shield bolts can be 
removed, the upper parts of the field frames can be lifted, and the 
armatures removed or replaced. 

18. There shall be no wires carried to the exterior of the frames, 
but the internal arrangement shall be such that the connecting wires 
can be suitably carried to their proper contacts with the machine as- 
sembled. These wires will be carried in conduit pipes which will tap 
directly into the lower part of the frames, but the frames need not be 
tapped by the builder unless specifically required. Two armature leads 
and one field lead will pass to the motor end; two armature leads and 
two field leads will be taken from the generator end. 

Rotary Compensators. 

These are machines built very much like motor generators and 
are used to change the voltage of one continuous current to other 
voltages of continuous current. Their particular action is more 
fully described under descriptions of various turret-turning systems. 
They consist in general of two complete machines with separate 
armature windings, commutators and brushes, and with separate 
magnetic fields. The armatures are mounted on a common shaft. 
In their first operation they are motors, but deliver currents to 
other motors at varying voltages by changing the excitation of 
their fields. 

Extracts from specifications issued by the ISTavy Department 
follow : 

" The compensator to be entirely enclosed and water-tight, but 
provided with openings of sufficient size and number to give easy 
access to the commutator, brush rigging and field coils, such open- 
ings to be provided with water-tight covers and clamping devices 
of approved construction. 

" The field frame will be of steel and enclose two separate mag- 
netic circuits; it will be separable in a horizontal plane through 



Dynamo Electric Machines 449 

the axis to permit of ready removal of armature and field coils. 
The two armatures will be carried on one shaft of ample strength, 
and forced ventilation or fans on the armature shaft will not be 
permitted. The compensator to be capable of wall or ceiling 
suspension. 

" Fields will be so compounded as to best adapt the machine to 
the purpose for which it is intended. The series winding is to 
compensate for the resistance drop in the armature and leads to the 
motors, and shall be such as to give as nearly a straight line com- 
pounding curve as possible. 

"The set to be designed for operation at 120 volts across the 
line. The maximum speed of the compensator must not exceed 
1500 E. P. M." 

A description of a rotary compensator as actually installed is 
given by the makers, the General Electric Company. 

Rotary Compensator. 

The rotary compensators are totally enclosed and consist of a 
common cast-steel magnet frame, containing two field magnetic 
circuits and enclosing two armatures mounted upon one shaft sup- 
ported in bearing heads at the outside ends. 

Magnet Frame. — The magnet frame consists of a cast-steel shell 
octagonal in shape and separable in a horizontal plane through the 
armature shaft. Steel bolts hold the halves of the frame together 
and feet are cast with the lower half for fastening the motor- 
generator set to its support. 

Openings are made at the top, sides and ends of the frame to 
give access to the brushes. The covers for these openings are all 
solid sheet metal made water-tight by rubber gaskets. The covers 
over the commutator and at the frame ends will be secured by wing 
bolts, thus making them easily removable for inspection and adjust- 
ment of the brushes. 

Pole Pieces. — Four laminated steel pole pieces in each frame 
support and retain the field coils and are held in position by bolts 
passing through the magnet frame. 

Armature Bearings and Linings. — The armature bearings of the 
self-oiling and self-aligning type, are cast with the end shields 



450 Naval Electricians' Text Book 

which fit accurately bored seats in the ends of the magnet frame. 
Oil rings supply ample lubrication, and a combination sight and 
overflow gauge is provided with each bearing of such a height that 
oil will not overflow inside the magnet frame. Holes in the top of 
the bearings, furnished with suitable covers, provide means for fill- 
ing the oil wells and inspecting the oil rings and provision is made 
for drawing the oil from the reservoirs. 

The split linings are of bronze and held from turning by dowel 
pins. 

Field Coils. — The field coils fit around and are held in place by 
the pole pieces. They are insulated with pressboard and varnished 
cambric and then treated with several coats of insulating baking 
japan, making them thoroughly water-proof. The ends of the 
windings are soldered to connectors. The fields of both machines 
are compound wound, the shunt being over the series. 

Armatures. — The armatures are of the multiple drum type 
having laminated steel cores, with air ducts for ventilation, sup- 
ported on cast-steel spiders separately keyed to the shaft with 
commutators at the ends. The cores are slotted to receive the 
armature coils, the slots being punched in the laminations before 
being assembled. The coils are form wound, thoroughly insulated 
with oiled muslin, tape and japan, and securely held in the slots of 
the armature core by binding wires. 

Commutators. — The commutators consist of hard drawn copper 
segments carefully insulated with mica and supported on cast-steel 
shells which are securely keyed to the shaft. The ends of the 
armature coils are soldered into the commutator segments. 

Brush Rigging. — The brushes of carbon and of ample cross- 
section are carried in brush holders supported on four insulated 
brass studs bolted to an adjustable yoke. The brush holders are 
supplied with adjustable springs for regulating the brush tension 
and alternate studs are connected by bus rings. 

Series Field Shunt. — The adjustable shunt on the series field 
consists of a slate having two terminals about 10 inches apart, upon 
which German silver strips can be bolted, the adjustment to suit 
ship conditions, being obtained by changing the number or section 
of these strips. 



Dynamo Electric Machines 451 

Cables and Connections. — The frame is to be supplied amdrilled 
so that it can be tapped for conduit by purchaser for armature and 
field leads to suit ship conditions. 

External Field. — There will be no appreciable field at a distance 
of 15 feet from the machine in any direction. 

Non-Corrosive Parts. — All small screws, nuts, etc., which are 
liable to become corroded and thus broken in removal are to be 
made of non-corrosive metal and not of iron or steel. Flat springs 
are to be of phosphor bronze, and spiral springs of steel, copper- 
plated. 

Tests. — The compensator will be subjected to the following tests : 

(1) With the two shunt fields connected in parallel across the 
line, the armatures being in series, the set is to be run without 
load for a continuous period of three hours. At the end of this 
time the temperature rise of the shunt fields must not exceed 50° C. 
measured by resistance. 

(2) The set to be immediately started and run under conditions 
of full* current and maximum voltage in the large motor (corre- 
sponding to minimum current in the field of armature for operating 
small motor) for a continuous period of one hour. 

(3) Within one-half hour after completion of test (2) the set 
is to be run for a period of one hour under conditions of minimum 
compensator voltage and full current to large motor. 

The temperature rise under the above conditions shall not ex- 
ceed the following: 

Series field 70° C. by thermometer. 

Shunt field 50° C. by resistance. 

Commutator 65° C. by thermometer. 

Armature 60° C. by 

Bearings 35° C. by 

Other parts 60° C. by 

In addition, the compensator is to be subjected to an overload 
of 50 per cent for five minutes under the conditions specified in 
(2) and (3) above. 

All windings are to withstand 1500 volts alternating for one 
minute. 

Weight. — The approximate weight of the set is 3000 pounds. 



452 Naval Electricians' Text Book 

Dynamotors. 

These are machines for supplying continuous currents at various 
voltages. They differ from motor generators in the fact that they 
have but one field for both the motor and generator while the motor 
generator has a separate field for each. This makes a much better 
balanced arrangement than the two fields of the motor generator, 
as all armature reactions are neutralized; there is no tendency to 
spark at the brushes and the brushes do not have to be shifted for 
changes of load, as all reactions due to generator characteristics 
are balanced by those of the motor which act in a contrary sense. 
Any change in the field affects both motor and generator, and will 
simply make them run faster or slower. 

The armature coils are wound on the same core, and in general 
the coils of the motor are wound first and imbedded in slots. Those 
for the generator wound over them are connected to a commutator 
at the opposite end from the motor connections. 

Dynamotors are used on shipboard for reducing the voltage of 
the main generators to lower values for use with the different 
systems of interior communication. 

They are -J horsepower and take about 3 amperes at 125 volts, 
transforming to 20 volts for general alarm bells and by adding 
auxiliary brushes, 13.3 and 6.6 volts may be obtained for call bell 
or other work. 

Rotary Converters. 

These machines are constructed for changing a continuous cur- 
rent into an alternating current, or vice versa. Like motor gener- 
ators, they may be built with separate armatures and commutators 
with separate fields or with but one armature with one winding and 
one field, fitted with two commutators, one for continuous current 
and one for the alternating current. 

In those built as two separate machines with the armatures 
secured to one shaft, the action is simply that one may be used as 
a continuous-current motor to deliver alternating currents at the 
other commutator, or alternating currents may be supplied to drive 
one, delivering continuous current at the other commutator. 

The case of one armature with one winding with connections to a 



Dynamo Electric Machines 453 

commutator and collector rings, one connection for continuous cur- 
rent and for alternating currents, requires some explanation. 

Let Fig. 208 represent a single ring armature revolving between 
a pair of magnetic poles, two opposite points being connected with, 
collecting rings, C and C, upon which brushes make contact to take 
off the current. 

When the armature is in the position shown, all the wires on each 
half are sending current in the same direction, and let the winding 
and field be such that it is up in both halves, making the outer 
ring C positive and the inner one negative. 




Fig. 208. — Diagram of Rotary Converter. 

Xow suppose the armature has turned a quarter turn, then, as 
before, all the wires on each side are trying to send current towards 
the top, but the connections to the rings have turned with the arma- 
ture and there is no connection at the top to take it off. The 
E. M. F's. generated on the two sides of each half are opposed and 
exactly equal, so there is no net E. M. F. between the collecting 
rings and there is no current at that instant. Between the posi- 
tions when the connections are vertical and horizontal the E. M. F. 
and current vary more or less uniformly. 

Xow suppose the armature is provided with a commutator, each, 
section of the armature connected to a commutator bar, and with 
brushes B and B, which make contact with the commutator seg- 
ments. These brushes make contact with different segments of 
the commutator as the armature revolves, while C and C always 
make contact with but one section of the armature winding. 

It is seen then that the armature wires between B and B all 



454 Naval Electricians' Text Book 

tend to send current in the same direction at all positions of the 
armature, so that a continuous current may be taken from B and B, 
while at the same time an alternating current may be taken from 
the same armature by C and C. 

Since either a continuous or an alternating current may be ob- 
tained from the same armature, it makes no difference what causes 
the armature to rotate, and therefore if continuous current be 
applied to the brushes B and B alternating current may be taken 
from the brushes C and C; and similarly, if alternating current be 
supplied to the brushes C and C the machine will run as an alter- 
nating current motor and continuous current taken from B and B. 

Relation of Voltages between the Continuous Current and Alter- 
nating Current Brushes. — From Fig. 208 it is seen that the alter- 
nating voltage is at a maximum when the armature coils connected 
with the collecting rings are also connected with the continuous 
current brushes, and therefore the maximum value of the alternat- 
ing voltage is equal to the steady value of the continuous voltage. 
The mean value of the alternating voltage is only 70.7 per cent 
of the maximum, while the actual values vary from zero to the 
maximum. 

Different Phase Currents. — A rotary converter with only two col- 
lecting rings as shown, would give a single-phase current. Two- 
phase currents could be obtained by having a second pair of col- 
lecting rings connected to the armature windings at points midway 
between the first ones. The E. M. F. between one pair would be a 
maximum when that between the other pair was at zero. The cur- 
rents would then be at right angles and the effective values of the 
E. M. F's. would be equal. By connecting three collecting rings 
to three equidistant points a three-phase current could be obtained 
from a rotary. 

In the three-phase current, the effective voltage between any 
two of the collecting brushes is 62 per cent of the continuous 
voltage. 

Rotary Connectors for Wireless Sets. 

These machines are of the two-field, two-armature type, with one 
end fitted with a commutator for continuous currents and the other 



Dynamo Electric Machines 455 

with collector rings for alternating current. The armature is 
driven as a motor by continuous current from the ship's power 
mains, driving the other as alternator. 

The object to be gained is simply the conversion of continuous 
current into alternating current for use in the primary of induction 
coils used in wireless sending apparatus, without much change in 
potential. It is usual to insert variable resistances in the field of 
each armature so as to vary the voltages of each within small limits. 

Size of Converters. — Converters are rated according to their 
output capacity expressed in kilowatts. Thus a 5-kilowatt con- 
verter is one whose product of E. M. F. at the terminals and output 
current is equal to 5000 watts or 5 kilowatts. Thus one form used 
has an input of 125 volts with 52.5 amperes and an output of 110 
volts and -15.5 amperes, or practically 5 kilowatts. 






CHAPTEE XXI. 

TESTS AND EXPERIMENTS WITH DYNAMO ELECTRIC 
MACHINES. 

The general idea of making tests of a completed machine is to 
discover whether it complies with the specifications under which it 
was constructed and is able to supply a certain amount of power. 
At the same time, it is by actually experimenting with electrical 
machines that a sound knowledge of their underlying principles 
may be most readily gained. 

General Tests. 

As a matter of procedure in making tests of dynamo electric 
machines the following list gives a general indication of the points 
to be considered: 

1. The general study of the machine. 

2. Mechanical strength of parts against breaking. 

3. Balance of armature. 

4. Sparking at the brushes. 

5. Noise. 

6. Eesistances of the various windings; armature, field, etc. 

7. Characteristic curves for internal, external and total circuits. 

8. Variation of speed under different loads and temperatures. 

9. Dielectric strength and insulation resistance. 

10. Heating. 

11. Efficiency. 

12. Determination of losses. 

13. Determination of E. M. F. around armature. 

Study of a Dynamo. 

Under this head the following general points should be particu- 
larly considered: 



Experiments with Dynamo Electric Machines 457 

1. Tabulation of electrical and mechanical points of design. 

2. Adjustment and fit of parts. 

3. Lubrication. 

4. Workmanship and material. 

A careful inspection of the machine should be made while at rest, 
noting every point connected with the field, armature, commuta- 
tor, brushes, brush rigging, headboard, etc., so that facts ascertained 
can be compared with the specifications, or if none are furnished, 
the points developed will help to make a complete description of 
the machine. 

The general form of the field frame should be noted with the 
number of field spools and poles, also the method used to connect 
the terminals of the windings from one field spool to another. 
The number of the terminals on each spool will indicate the form 
of field winding; whether series, shunt or compound. If a com- 
pound machine it will be seen whether the two windings are sepa- 
rate or one on the other, noting which is on the outside. An 
inspection will show whether the pole pieces and magnet core are 
in one with the field frame or whether they are separate and 
bolted together. 

The construction of the armature would show its type of wind- 
ing, whether ring or drum, and the fact should be noted whether 
the conductors are wound directly on the armature core or are 
imbedded in slots. The commutator segments should be counted 
and the method of securing the armature windings to them noted ; 
that is, whether they are clamped, screwed or soldered. 

The kind and number of brushes should be noted and the me- 
chanical design of the brush holders and the means employed to 
move all the brushes together should be examined. The brushes 
should be removed and replaced to become familiar with the various 
springs and attachments and the brushes should be rocked back and 
forth by the rocker arm and clamped in different positions. 

The headboard should be inspected and the different terminals 
marked, so that the series and shunt terminals and armature and 
equalizer leads can be readily distinguished. This will also show 
whether the machine is a long shunt or short shunt in case it proves 
to be a compound machine. 



458 Naval Electricians' Text Book: 

The maker's name-plate furnishes important information, such 
as the power expressed in kilowatts, the revolutions of the armature 
per minute to produce the required E. M. F., the E. M. F. at the 
terminals, the current output, type of field winding, etc. This 
information should be tabulated to be verified by tests and 
experiments. 

Adjustment and Fit of Parts. — The adjustment and fit of all 
parts should be carefully examined and particular attention should 
be given to the brush rigging. Brush holders ought to be readily 
accessible for adjustment and renewal of brushes and springs, and 
adjustable for tension, generally without tools, and constructed 
to admit of proper staggering of brushes. 

Lubrication. — All bearings should be provided with oil wells of 
sufficient capacity and inspection should be made to see if any 
arrangement is provided to prevent oil running along the arma- 
ture shaft. The best practice requires self -oiling bearings provided 
with split babbitted bearing linings, and visual oil gauges for 
determining the amount of oil in pockets and drains for drawing 
off oil. 

Workmanship and Material. — Naturally the materials and work- 
manship of all parts of any machine should be of the best quality, 
and notes should be made of any particular part that shows evidence 
of inferior workmanship or defective or cheap material, and all 
windings should be carefully observed for any signs of abrasion 
of the insulation or outside covering. Special attention should be 
given to the workmanship and material of the brush rigging and 
springs. The best practice requires all metal portions to be non- 
corrosive and fitted with flexible connections between brush and 
holder. Brushes should be carefully examined and their quality 
should be such as to give perfect contact without cutting, scratching 
or smearing the commutator. 

Mechanical Strength. 

All the main parts of dynamo electric machines as the base, field 
frames, field magnets, armature, shaft, bearings, etc., should be of 
such strength that they will not spring with any reasonable force. 
The strength to resist centrifugal forces due to the armature revo^- 



Experiments with Dynamo Electric Machines 459 

lution should be tested by running the armatures to at least double 
their normal speed without load, and series motors should be run at 
four times their full-load speed. There should be no signs of 
weakening of any part of the armature when run at these in- 
creased speeds for at least thirty minutes. 

Balance of Armature. 

Before commencing any test requiring the movement of the 
armature, carefully turn it by hand or jack over the engine if di- 
rectly connected to its shaft, looking at the same time for any 
obstruction to free movement. When satisfied that all is clear make 
ready for slowly turning over the armature with the motive power 
supplied. 

In case of a steam engine, either directly driven or by means of 
a belt, see the oil service in working order, and take all the usual 
precautions in starting the engine; exhaust open, water clear of 
cylinders, drains and relief valves open, bearings oiled and that the 
cylinders have been properly warmed. In turning over the arma- 
ture for the first time make sure that the external circuit is opened 
and that the brushes are raised clear of the commutator. 

Open the throttle and let the engine turn slowly and watch the 
revolution of the armature, noting whether it revolves concentric- 
ally ; that it does not strike the pole pieces at any point ; that there 
is equal clearance between armature and the pole pieces all around 
and that it runs smoothly and free from undue vibration. The 
alignment of the shaft should be noticed and one not true would 
soon manifest itself by heated bearings and these must be watched 
from the time the engine is started. 

The perfection of balance of armatures of generators should be 
tested by running them at least 25 per cent above their normal 
speed; of shunt motors at their normal speeds; of series motors 
from normal to double their rated speeds, and of compound motors 
from normal speed to 50 per cent above normal. In all cases the 
armatures of well-designed machines should not show the slightest 
vibration. 



460 Naval Electricians' Text Book 

Sparking at the Brushes. 

The causes of brush sparking are given in Chapter XXXI and 
if any sparking occurs during a test, its cause should be sought and 
the machine credited with a defect. Modern well-designed gener- 
ators and motors should show no signs of sparking whatsoever under 
any changes of load within their capacity and generators under 
ordinary conditions should show no sparking when overloaded 25 
per cent, nor should any change in the brushes be a necessity to 
prevent it. 

Motors to run in the open should show no signs of sparking from 
no load to full load and enclosed motors from no load to 25 per 
cent overload and without shifting the brushes. No sparking 
should also hold under all conditions of weak or strong field. 

Noise. 

All armatures of generators and motors should run at their full 
rated speed and load practically without noise or humming sounds 
and without rattling or chattering of the brushes. 

Resistance of Windings. 

The ohmic resistances of all parts of the armature windings, 
series and shunt windings should be carefully measured and re- 
corded so that the values of the fall of potential through the 
various circuits can be checked and the calculated value of the 
external energy compared with that actually obtained. 

!A method for measuring these resistances is given in the chapter 
on Measurements. All the different methods used for measuring 
such small resistances as that of a large armature or the series 
winding are based on the " fall of potential " method and require 
the use of some standard small resistance, and the accuracy of the 
measurement depends on that of the standard resistance. The 
method described in the chapter referred to is available for use on 
board ship with the instruments usually furnished, but if a labora- 
tory is available other methods can be used with possibly more 
accuracy; and such is one given below. 



Experiments with Dynamo Electric Machines 



461 



Measurement of Armature Resistance by Comparison of De- 
flections. — This depends on the following general principle : If 
two resistances hare the same current flowing in them, the differ- 
ences of potential at their ends is proportional to their resistances. 




Fig. 209. — Measurement of Armature Resistance. 



In Fig. 209 

D is the armature and resistance, 

R 1 standard resistance, approximately equal to that of D, 

R 2 variable resistance, 

C one or two cells (preferably secondary cells), 

G galvanometer, 

S switch, 

1, 2, 3, 4, 5, 6 terminals of a double-pole, two-throw switch. 

The leads of the circuit containing the cells are connected to 
the brushes, disconnecting the field windings. The wires from 
the armature to the galvanometer are connected between the 
brushes and the commutator, making sure that the wires press on 
opposite segments and make contact with one segment only. 

The galvanometer should have a uniformly divided scale and its 
reading should be proportional to the deflecting current. If it is a 



462 Naval Electricians' Text Book 

very sensitive one, it may be necessary to use a shunt, or a resist- 
ance in series with it will often give the desired result. 

The resistances of the leading wires to the galvanometer does not 
affect the accuracy of the measurement as they are so very small 
compared with that of the galvanometer, and the latter may be far 
removed from the machine where it will be free from any influences 
other than the deflecting current. 

Instructions for Test. — Close the switch S and by means of the 
switch hinged at 2 and 5 connect the galvanometer to 1 and 6, so 
that it is connected to the circuit containing the standard resist- 
ance. Adjust resistance R 2 to get a good readable deflection. 
Note the deflection on the scale of the galvanometer. Eeverse 
the switch to 3 and 4, connecting to armature and note the deflec- 
tion. Eeverse the switch and repeat the first reading, and repeat 
the whole operation five or six times. 

Let d ± be the mean of all the deflections when connected to R x , 
d 2 be the mean of all the deflections when connected to D, 
V x the fall of potential through R x , 
V 2 the fall of potential through D. 
Then 

d 2 ~ r 9 > 

and by the principle stated above 

or 

R, d, j r\ ^i d„ 

D d 2 d x 

Connecting the leading wires from the galvanometer to the 
brushes will give the resistance of armature, brushes and contacts, 
and subtracting this value from the armature resistance will give 
the resistance of brushes, brush holders and contacts ; an item some- 
times of great importance. 

This method is suitable for measuring resistances between .1 and 
.001 ohm, but for resistance lower than these values, other methods 
must be resorted to, such as that by the Thompson bridge, which 
will measure as low as .0001 ohm. 



Experiments with Dynamo Electric Machines 463 

Measurement of the Resistance of Field Windings — Series Wind- 
ing. — As this is of very low resistance, either the method given in 
the chapter on Measurements or the method given above may be 
used, inserting the series winding directly in series with the cell 
circuit. 

Shunt Winding. — Either of the two methods given in the chapter 
referred to may be used, viz., by the Testing Set or Bridge, or by 
the Voltmeter and Ammeter method. 

In measuring the resistance of the shunt winding, it is usual to 
measure both the cold and hot resistance. The voltage applied to 
the shunt terminals should be the normal working voltage and 
readings of the voltmeter and ammeter should be taken at regular 
intervals of time. 























4U 




















130 






































120 





















10 20 30 40 50 60 TO 80 90 

Fig. 210. — Curve of Resistance. 

Curves plotted with intervals of time as abscissae and the resist- 
ances obtained at the corresponding time as ordinates are in- 
structive. Fig. 210 shows a curve obtained in this manner. 

The numbers on the bottom line represent seconds of time and 
those on the left, resistance in ohms. This shows that the resist- 
ance at first increased rapidly with the time, then more slowly and 
became approximately constant after an hour's time of running, 
and the greatest value would be the hot resistance. 



Characteristic Curves. 

Characteristic curves of electrical machines have been referred to 
in the chapter on Generators, but it is the purpose here to go more 
into the details of the methods used in obtaining these curves and 



464 



Naval Electricians' Text Book 



to show graphically the necessary connections for making this part 
of the electrical tests. 

The following curves are the most important ones for which 
data are taken for tests or experiments on generators of the classes 
named: Series generator: external circuit; total circuit; mag- 
netization. Shunt generator: external circuit; internal circuit; 
total circuit; armature. Compound generator: compound; differ- 
ential series, external circuit; internal circuit. 

Characteristics of a Series Generator. — The curve usually ob- 
tained by observation is the external circuit curve as this can be 
found by connecting up a voltmeter to show the fall of potential 
in the external circuit, and by including an ammeter in the circuit. 
The connections are shown in Fig. 211. 



A/VW 







©J-Vvw 



Fig. 211. — Connections for External Circuit Characteristic of Series 

Generator. 



The voltmeter V is connected to the terminals of the machine 
(note, not to the brushes) and the ammeter A is included in the 
main circuit in which there is a variable resistance R. 

Instructions. — Add resistance in R until both the E. M. F. and 
current are quite small, and take simultaneous readings of both 
instruments and record them. Then vary (decrease) R by suc- 
cessive amounts so that successive points on the curve can be ob- 
tained, it being generally advisable to make the reading an even 
number of amperes for convenience in plotting. This operation 
can be carried on up to the safe carrying capacity of the machine. 

For any given value of current a small change of speed produces 
an approximately proportional change of E. M. F., so if the speed 
varies, which should be tested at each reading by a tachometer, the 



Experiments with Dynamo Electric Machines 465 

voltmeter readings should be corrected to some convenient constant 
speed near the mean. 

With the data obtained plot the amperes as abscissae and the 
differences of potential as ordinates, according to some convenient 
scale, and draw a fair curve through the points obtained. 

Then with the resistances of the armature and field, calculate 
the volts lost in the armature and field for each value of C, by the 
equation C (r a -f- r m ), see Chaper XII, and plot the internal resist- 
ance line. Then add these values vertically to each of the points 
on the curve corresponding to the values of C, which will give a 
series of points, through which the total circuit curve can be drawn. 
These curves are shown in Fig. 75. 



A/VV\A 




b 
Fig. 212. — Connections for Obtaining Magnetization Curve. 

Magnetization Curve. — This curve shows the relation between 
the exciting field current and the resulting E. M. F. produced by 
the armature at no load. 

The diagram of connections is shown in Fig. 212. 

The series field F is disconnected and the voltmeter V is con- 
nected to the brushes of the armature D. The field winding is 
connected to an outside source of E. M. F. of value equal to that 
produced by D. The change of exciting current may be effected 
in either of two ways and both are given for purposes of instruc- 
tion. E, a variable resistance may be changed, thereby effecting 
change of current in F, or the difference of potential at the termi- 
nals of F may be varied by the resistance R'. This is a resistance 
of sufficient carrying capacity not to become overheated when per- 
manently connected to the source of supply and also carrying the 
field current. The field winding is connected to one end of this 




466 Naval Electricians' Text Book 

resistance, a, and to a movable point c, which slides along ab. As 
c is moved towards a, the difference of potential between a and c 
decreases, consequently decreasing the current through F. 

Instructions. — Begin with the exciting current zero or very small, 
by varying either R or E' or both. Note the simultaneous readings 
of A and V. Vary the exciting current as desired and note the 
readings, and continue this until the maximum current in F is 
reached. Then decrease the current by similar steps. For each 
value of A read V ' , and note the speed of D. Eeduce the readings 
of V to some constant speed from the formula 

V ~ n' 
where V and ri are the E. M. F. and observed speed and V the 
desired E. M. F. and n the normal speed. 

With the observed values, plot 
curves as before, with current as 
abscissae and E. M. F. as ordi- 
nates for both ascending and de- 
scending values of exciting cur- 
rent. It will be found that this 
gives two distinct curves, and 
the failure of the two curves to 
coincide is due to the hysteresis 
of the magnetic circuit, and the 
distance apart of the curves will 
be an indication of the nature of 
the metal used in the circuit as 
regards hysteresis. Soft iron 
shows little hysteresis while hard iron or steel shows the effect very 
strongly. 

The form of the magnetization curve resembles very closely that 
of the total circuit curve of the series machine, which should be 
natural, as the E. M. F. is directly proportional to the magnetiza- 
tion and that in turn to the amperes of the exciting current. 

Characteristics of a Shunt Generator — Internal Characteristics. 
— The curve of the internal circuit is obtained by disconnecting the 
external circuit; that is by leaving it open, when the machine 



-H0> 



Fig. 213. — Connections for Obtain- 
ing Shunt Internal Characteristic. 



Experiments with Dynamo Electric Machines 467 



R' 




^a 



practically becomes a series machine with the external circuit short- 
circuited, so the resulting curve should show the general form of 
the series total or magnetization curves. 

The connections to be made for obtaining the necessary data are 
shown in Fig. 213. 

The terminal a of the shunt field F with its regulator is discon- 
nected from b and between these points is inserted the variable 
resistance R with ammeter A in circuit. This resistance is added 
to allow a greater change of voltage and resulting current so as to 
obtain more points on the curve. 

Instructions. — It is well to 
start this experiment with very 
little magnetization, or with 
all resistance in the regulator 
and R. When the armature is 
running at its normal speed, 
and all resistance in, take read- 
ings of A and V. Then vary 
the resistances till the ammeter 
shows an even number of am- 
peres as 5 or 10, and read V, 
checking the speed at the same 
time. Then make A read 10, Fm 21 ^_ Connections for obtaining 
then note V and so on up to Shunt External Characteristic, 
the safe carrying capacity of F 

or to the point of saturation of the magnets. Correct all speeds to 
that of the mean speed as previously explained. 

With the data, obtained, the curve can be plotted in the usual 
way with amperes as abscissa? and volts as ordinates. If the experi- 
ment was commenced with low resistance or high magnetization 
and the current stepped down, the resulting curve would be slightly 
different from the first and as the curves are all for the purpose of 
comparison, it is better to take them starting from the same point; 
that is, with either increasing or decreasing magnetization. 

External Shunt Characteristic. — The connections for obtaining 
the necessary data for this curve are shown in Fig. 214. 

There are no changes in the connections of the machine itself, 







468 Naval Electricians' Text Book 

but the variable resistance R is introduced in the external circuit 
with the ammeter in circuit. 

Instructions. — At first leave the outside circuit open and adjust 
the regulator in the field so that the generator at normal speed will 
give the normal E. M. F. This gives the first point on the curve, 
zero current and maximum E. M. F. Do not change the regulator 
resistance during this experiment. 

Close the external circuit through switch S with enough resist- 
ance in R to give a small resulting current in external circuit. 
This is a matter of simple calculation, knowing the E. M. F. and' 
the current desired, the amount of resistance is readily known. 

Eead both A and V and note speed. Vary R for a new value of 
A and note the simultaneous readings and take the revolutions 
to be corrected as in other cases already described. 

It is more than probable that starting as above, the safe-carrying 
current will be reached before the curve can be completed; that is, 
before the E. M. F. falls sufficiently to cause its resulting current 
to drop. In this case start with a lower E. M. F. on open circuit 
by changing the regulator and then the complete curve may be 
obtained. 

The general form of these curves is shown in curve 1 (Fig. 78) 
and also the method of obtaining the other curves from this one. 

Precautions. — To obtain good results, care should be taken not to 
break the circuit or to make too large changes in the variable 
resistance. 

If at any time a new point is further from the last one taken 
than desired) it is better not to go back, for the curves for increasing 
and decreasing magnetization are different. 

If the external circuit should be broken while working on the 
lower part of the curve, the magnetization would run up at once 
and if the circuit was now closed through the same resistance, there 
would be danger of getting an excessive current before the mag- 
netization would fall to its previous state. In this case it would 
be better to throw all resistance in before closing the switch and 
then gradually reduce it till the conditions are the same as before 
the break. 

When the resistance is nearly all out so that the E. M. F. has 



Experiments with Dyxamo Electric Machines 4G9 

fallen, bringing the lower end of the curve near the current line, 
the curve for increasing magnetization may then be started without 
any break of circuit or change of any kind, and if care is exercised 
and the change of resistance is very small and gradual, the two 
curves can be completed, forming a loop at the lower end. 

If the up curve is to be started first, the field circuit should be 
left open before closing the external circuit, or short-circuiting the 
brushes (all the external resistance being out). After the external 
circuit is closed the field circuit can be closed, for then the E. M. F. 
at the brushes and current in the field is almost zero. The value 
of current for zero potential at the brushes depends upon the 



51 ' & 

^-TLVXAAAAA/W^-ri-^ 



/O 



Fig. 215. — Connections for Obtaining Armature Characteristic. 



resistance of the armature and the E. M. F. due to residual mag- 
netism. If the field excitation is gradually reduced from a high 
value to zero, the E. M. F. due to residual magnetism will have a 
higher value than when the circuit is suddenly broken. 

The increase in resistance of the field coils due to increase in 
temperature affects the resulting curve as does also self-induction 
and armature reactions and as every effect has its cause, much 
may be learned by the experimenter in taking these curves. 

Armature Characteristic. — This is a curve that shows the rela- 
tion between the external current and the field current when the 
difference of potential at the terminals is kept constant and is 
useful in studying the compounding of a generator, the departure of 



470 



Naval Electricians' Text Book 



the curve from a straight line showing the change in the field cur- 
rent to be compensated for by series turns on the shunt machine. 

The connections for making the test is shown in Fig. 215. 

An ammeter is connected in the field circuit and the usual 
variable resistance R in the external circuit. 

Instructions. — Adjust the E. M. F. at the brushes with the 
external circuit open to the value at which the difference of poten- 
tial is to be kept constant. Then close the external circuit through 
the maximum resistance used, adjust the field regulator so as to 
give the same E. M. E. as before and then read A and V. Change 




EXTERNAL CURRENT 

Fig. 216. — Armature Characteristic. 



the resistance R slowly, adjust the E. M. F. to its constant value, 
and read A and V. The curve will have the general form shown 
in Fig. 216. 

The distance 1, 2 on the scale of field current shows the field 
current that must be added by series turns to produce an E. M. F. 
of the external current 03 equal to the original E. M. F. producing 
field current 04. 

Characteristics of a Compound Generator. — The compound ma- 
chine, being merely a shunt generator with the addition of a series 
field of a few turns, may be used as a shunt generator by leaving 
out the series coils. The connections are then made and the 
external and internal characteristics are then obtained as previously 
described under the shunt generator. 



Experiments with Dynamo Electric Machines 471 

To obtain the series characteristic the shunt field is disconnected 
and the procedure is the same as given under the Series Generator. 

Compound Characteristic. — The connections for obtaining the 
data for plotting the compound characteristic curve is shown in 
Eig. 217. 

This shows a " long shunt " machine with the voltmeter V con- 
nected across both armature D and series field F' and the ammeter 
in the external circuit. 

Instructions. — Before closing the external circuit adjust the 
E. M. F. to the same value as that for the external shunt char- 
acteristic, so the two curves will start from the same point on the 




/^SM/WV 



75 



£ 



Fig. 217. — Connections for Obtaining Compound Characteristic. 



ordinate axis. When the field regulator is once adjusted to give 
the proper voltage do not change it during the experiment. 

Close the external circuit through a resistance that will give a 
small current and take simultaneous readings of A and V, and at 
same time take the speed to reduce the voltage to the normal speed. 
Proceed by small changes in the resistance B and obtain values 
for A and V. 

By disconnecting the series coils and connecting them so that the 
current through them is reversed, the differential curve is obtained. 
As the field is weakened by increase of current in the series coils, 
which oppose the shunt, the curve drops more rapidly than the 
external shunt and the maximum current is much smaller. 



472 



Xaval Electricians' Text Book 



Curves showing the relative differences between the character- 
istics of a compound generator are shown in Fig. 218. 

Variation of Speed. 

The allowable variation of armature speed of dynamo electric 
machines under different conditions of load and temperature de- 
pends on the kind of work for which they are designed. Modern 
well-designed machines should show very close regulation of speed, 



130 




20 40 60 80 100 120 140 

Fig. 218.— Characteristic Curves of a Compound Generator. 



and as illustrating the amount of variation considered to be practi- 
cal, the specifications for machines used on ships of the navy are 
quoted. 

For main generators the speed variation must not exceed 2-J 
per cent when load is varied between full load to 20 per cent of 
full load, gradually or in one step, engine running with normal 
steam pressure and vacuum. A variation of not more than 3-J per 
cent is allowed when full load is suddenly thrown on or off the 
generator, with constant steam pressure, either normal or 20 per 
cent above normal. A variation of not more than 3J per cent is 



Experiments with Dynamo Electeic Machines 473 

allowed when 90 per cent of full load is suddenly thrown on or off 
the generator, with constant steam pressure at 20 per cent below 
normal; exhaust in both cases to be either into condenser or 
atmosphere. 

For shunt-wound motors, the variation in speed from no load to 
full load is not allowed to be more than 12 per cent in motors of 
less than 5 horsepower and not more than 9 per cent in motors of 
5 horsepower and above. Series and compound-wound motors must 
make their rated outputs at their rated speeds. The motor must 
be designed to obtain its rated speed when hot, with atmospheric 
temperature of approximately 25° C. and the speed actually ob- 
tained at the end of a heat run must be within 4 per cent of the 
rated. The variation in speed due to heating should not exceed 
10 per cent. 

For motor generators of a speed of about 2000 revolutions per 
minute, such as used for gun-elevating equipment, the speed varia- 
tion between no load and full load and from full load to no load 
should not exceed 10 per cent of normal. For those of about 1500 
revolutions per minute, used in turret-turning equipment, the 
variation between no load and full load and from full load to no 
load should not exceed 6 per cent of normal. 

For motors for driving machine tools, the variation in speed from 
no load (hot) to full load (hot) shall not be more than 9 per cent 
in motors of less than 5 horsepower and not more than 7 per cent 
in motors of 5 horsepower and over. For all motors the variation 
from their rated speeds at full load (hot) must not exceed 5 per 
cent and the variation in speed due to heating must not exceed 
10 per cent. For variable speed motors these conditions must be 
met at any set speed throughout the range. 

Dielectric Strength and Insulation Resistance. 

There are two distinct properties which the insulation of a 
completed machine should possess : first, its ability to withstand 
the application of a high voltage for a long time without deterio- 
ration, its dielectric strength; second, its ability to offer a suffi- 
ciently high resistance to prevent any appreciable leakage in work- 
ing, its insulation resistance. 



474 Naval Electricians' Text Book 

The insulation of a generator or motor should first be tested by 
the application of an alternating E. M. F. 5 to 10 times the work- 
ing pressure of the machine, applied between one of the main ter- 
minals and the frame. This will make sure that all conductors are 
insulated from the iron parts of the machine. Naval specifications 
for generators and motors require the test for dielectric strength 
to be made at the end of a heat test with pressures of at least 1500 
alternating volts to be applied for a continuous period of one min- 
ute, the source of power to be either a generator or transformer of 
at least 5 kilowatts capacity. 

Several methods of measuring insulation resistance are given in 
the chapter on Measurements and also in the chapter on Care of 
Electric Plant and Accessories, but specifications for modern ma- 
chines require a testing voltage of at least four or five times the 
difference of potential ordinarily to be withstood. The insulation 
between all parts should be at least one megohm. 

Heating. 

The heat produced in the conductors of electric machines, in 
the armature and field windings, commutator segments, in the iron 
frame work, the field frame, spools and pole pieces, bearings, etc., 
is energy lost and consequently it is the aim to reduce these losses 
to a minimum. Different rises of temperature are allowed in dif- 
ferent classes of machines, depending on their construction and 
their location, the general limits being between about 30° C. to 60° 
C. after four hours' continuous running at full load. The rise in 
temperature in enclosed motors is allowed to be about 10° C. 
greater than in open motors. 

For generators used in the navy the maximum allowable rise in 
degrees C. is armature 33J°, commutator 40°, field coils 33^° above 
a standard room temperature of 25° C. 

Rise of Temperature. — It is usual to measure the rise of tem- 
perature in the armature and field coils by means of the change of 
their resistances due to the heat produced and in the commutator 
and other parts by means of a thermometer. 

By Thermometer. — In using the thermometer great care should 
be used to see that the bulb is well protected by waste or some such 



Experiments with Dynamo Electric Machines 475 

covering to prevent radiation and that trie highest temperature is 
taken. It is obviously impossible to measure the temperature of 
coils by a thermometer with any degree of accuracy whatever, as 
the inner layers, which experiment always shows are the hottest, 
cannot be reached by ordinary thermometers. Difficulty would also 
be found in getting the hottest part of outside layers as some parts 
would be cooled by the moving armature more than others. 

The thermometer should have a long thin bulb and be placed flat 
against the surface with as much bearing surface as possible, and 
well covered with some non-conducting material and if possible 
should be read in this position. 

By Change of Resistance. — To measure the rise in temperature 
of armature or field conductors, their resistances are measured, as 
already given, both when hot and cold; that is, the resistances are 
measured when the machine is at rest and again after four or five 
hours' continuous run at full load and before they have had time 
to cool. 

Method of Calculation. — The method of calculation in general 
use and required by navy specifications is that based upon the 
report of the Committee on Standardization of the American Insti- 
tute of Electrical Engineers and is as follows : 

1. In computing the temperature rise of a coil by change of 
resistance, the following method should be used : 

(a) The total rise in temperature of a coil during a test to be 
determined by the formula adopted by the American Institute of 
Electrical Engineers, viz. : 

Bz= (238 + 0(%*- } — l) 

where 6 = total rise of degrees Centigrade, 

t = cold temperature of the coil, 
R t = cold resistance of coil, 
22 (t+e) = hot resistance of coil, 
also let T = final room temperature ; 

and by the use of this formula it is assumed that .0042 is the 
temperature coefficient of copper from and at 0° C. 

(b) From the total temperature rise calculated as above, sub- 
tract the difference between the cold-coil temperature t and the 



476 Naval Electricians' Text Book 

final room, temperature T, which should he carefully taken as 
directed below. 

(c) The rise thus obtained above final room temperature to be 
corrected by one-half of 1 per cent for each degree Centigrade that 
the final room temperature differs from 25° C. The correction to 
be added if the room temperature is below 25° G. ? and subtracted if 
above it. 

In the case, however, of shunt- wound coils subjected to a con- 
stant potential, the current strength and therefore the temperature 
rise will be changed by a change of room temperature. A correc- 
tion for this should be made by correcting the rise, as above calcu- 
lated, in proportion as the final absolute temperature of the room 
differs from the absolute temperature at 25° C. In most cases this 
correction nearly neutralizes the correction under (c) ; both cor- 
rections are, however, recommended by the American Institute. 

2. In connection with the above method, the following instruc- 
tions should be carefully observed: 

(a) The temperature t should be taken by a thermometer placed 
directly on the coil, at the time the cold resistance is taken, and 
has nothing to do with the cold-room temperature. In taking this 
cold-coil temperature care should be taken that the coil has not 
been recently brought from a much colder or hotter place than that 
in which the test is being made. 

(b) The room temperature T, above which the temperature rise 
of the machine is calculated, must be very carefully determined. 
The temperature of the room should be read from a thermometer 
placed in such a position that it fairly represents the temperature 
of the air surrounding the machine. If 'the room temperature 
remains constant during the run there will be no question as to the 
final room temperature; if the temperature varies, however, as is 
usually the case, for a short run of two hours or less, the average 
of the entire run should be taken ; for a run of six hours or more the 
average of the last three hours should be taken. Conditions should 
be such that the room temperature will not vary greatly during the 
tests, and a variation in room temperature of over 10° C. during 
a heat run of six hours, or a proportionate change for runs of 
shorter duration, should in no case be exceeded. If, however, the 



Experiments with Dynamo Electric Machines 477 

temperature is very irregular throughout the run, or changes rapidly 
at the end, the test should he made over, especially if the machine 
is near the heating limits of the specifications. 

(c) To prevent the sudden fluctuation of room temperature due 
to the opening of doors, etc., it is recommended that the bulb of 
the thermometer registering the room temperature be inserted in 
a hole drilled in a small iron block, the hole to be filled with 
cylinder oil or mercury. This block can be conveniently made of 
about the following dimensions : Three inches in length, 2 inches 
in diameter, with a J-ineh hole, drilled 1J inches in depth. Care 
should be taken that the machine under test is not exposed to 
drafts of air. 

3. An example of the above follows: 

Length of heat run = 6 hours. The last seven half-hour read- 
ings of room temperature are, 19.5, 20, 20.5, 21, 21.5, 22, and 22.5; 
average, 21° C. = T. 

The cold resistance of coils = 150 ohms = Rt • 

The hot resistance of coils = 180 ohms = R(ne)- 

The cold temperature of the coils is 15° C. 

Then = (238 + 15) (^ —l) = 50.6° == rise above cold- 
coil temperature. 

The variation from cold-coil temperature to final room tempera- 
ture is 6 degrees. Then 50.6° — 6° = 44.6° rise above room 
temperature. The difference between final room temperature and 
25° C. is 25° — 21° = 4°. Therefore, 4 times J per cent equals 
2 per cent correction, or 44.6 X 1-02 = 45.49° rise above room 
temperature corrected to 25° C. 

If the coils were shunt-wound constant-potential coils, the rise 
should be again corrected in the ratio of 238 + 21° and 238 + 25°, 
or a rise of 44.79°. 

4. In computing temperature rises from thermometer measure- 
ments, the rise should be figured above final room temperature T 
taken as explained in paragraph 2 (b) above, and corrected as 
directed in paragraph 1 (c) above. 



478 Naval Electricians' Text Book 

Efficiency. 

The question of efficiency of generators has been treated in the 
chapter on Efficiencies and Losses of Generators and of motors in 
the chapter on Motors. The efficiency of generating sets should 
be as high as practicable consistent with good design and the specific 
requirements, but where thorough reliability and freedom from 
danger of breaking down are the first requisites, as in motors for 
turning turrets, elevating guns, hoisting ammunition, hoisting 
boats, etc., maximum efficiency is often sacrificed to reliability. 

The commercial efficiencies required for the main generators 
installed on ships of the navy are given in the following table: 

tt w Loads. 



IV. vv. 

2.5 


11/3. 

Per Cent. 
78 


1. 

Per Cent. 

78 


Per Cent. 
76 


Per Cent. 
73 


5 


80 


80 


78 


75 


8 


83 


83 


81 


77 


16 


87 


87 


86 


84 


24 


88 


88 


87 


85 


32 


88 


88 


87 


85 


50 


89 


89 


88 


86 


100 


90 


90 


89 


87 






Commercial Efficiency of Generators. — The commercial efficiency 
is determined by finding the ratio between the power utilized in the 
external circuit and the total power supplied to the engine of the 
generator, both expressed in the same units. 

The methods used for determining the efficiency are of two kinds : 

(1) Methods in which the driving power and the electrical out- 
put are both separately measured. These are called direct methods. 

(2) Methods in which the losses in the generator are determined 
by electrical measurements. These losses added to the output gives 
the power supplied to it. These are called indirect methods. 

Direct Method. — For any given load the power utilized in the 
external circuit is found by inserting an ammeter in the circuit 
and connecting a voltmeter to the terminals of the machine. In- 
dicator cards are taken from all cylinders at the same time and 
the revolutions of the engine are taken. 

From the indicator cards, the mean effective steam pressure is 



Experiments with Dynamo Electric Machines 479 

found, and with the area of piston, length of stroke and number of 
revolutions, the indicated horsepower is found from the formula 

_ plan 
n - r '~ 33,000 > K) 

where p = mean effective pressure in pounds per square inch, 
I = length of stroke in feet, 
a = area of piston in square inches, 
n = number of revolutions per minute. 

Dividing the product of the volts and amperes of the external 
circuit hj 746 expresses the external energy utilized in horse- 
power, thus 

H.P.=-|iS (2) 

and the commercial efficiency = tt\ • 

Indirect Method. — In this method the losses in the generator are 
found and the efficiency is calculated from the formula 

ffl . output __ output 

J ~ ' input ~~ output -f- losses " 
The output is as before directly measured by means of a volt- 
meter and ammeter properly connected in the external circuit. The 
losses are partly calculated and partly found by experiment. 

The calculated losses are those due to power spent in overcom- 
ing the field and armature resistances. In each case and for each 
particular part, the loss in watts is equal to the square of the cur- 
rent multiplied by the resistance, or 

watts = C 2 R. 
Thus, for the 

armature loss, W = C 2 a r a ; 
series-field loss, W = C 2 m r m ; 
shunt-field loss, W = C 2 s r s ; etc. 

The losses found by experiment are those due to 

Friction of the bearings, brushes, air friction. 
Eddy currents in the armature core. 
Hysteresis losses in the armature core. 



480 



Naval Electricians' Text Book 



These losses can be determined by running the generator as a 
motor with no load, separately exciting the field to its normal 
extent and supplying the armature with current sufficient to. make 
it run at the same speed it did when running as a generator ; or, in 
other words, sufficient to impart to the armature terminals an 
E. M. F. equal to the total E. M. F. generated when run as a 
generator. 

The efficiency of a motor is the ratio of the input to the output, or 

„ . output input — losses 

efficiency = - — — r = — — : 1 • 

J input input 



V R2 

^AAAAA/VVWV 





Fig. 219. — Connections for Swinburne's Test. 



When the generator is run as a motor with no load and separately 
excited, the efficiency is zero, or 

input = losses. 

The losses now are the watts lost in the armature, due to the 
current producing the speed and the other losses referred to. The 
current and the armature resistance both being so small, the G 2 a r a 
is so extremely small as to be negligible, so the input is equal to the 
losses due to friction, hysteresis and eddy currents. 

The input is measured by a voltmeter connected to the armature 
terminals and an ammeter connected in the circuit. 

Swinburne's Test. — The connections for finding the current 
absorbed when supplied with an E. M. F. equal to that produced as 
a generator is shown in Fig. 219 and is known as Swinburne's test. 



Experiments with Dyxamo Electric Machines 481 

Connections are made as in Fig. 219, in which 
L X L 2 are the supply mains, 
D the armature under test, 
F the shunt-field coils, 

R x adjustable resistance for varying voltage at arma- 
ture terminals, 
R 2 adjustable resistance for regulating exciting current, 
V voltmeter connected across armature, 
A ammeter for measuring armature current, 
SB starting rheostat. 

Instruction. — With the resistance in R 2 all out, close the switch 
of SR. This throws in the shunt field and excites it and at the 
same time sends current through R t and the armature D, starting it. 

Adjust the resistance in R ± until the voltage shown on V is equal 
to that produced when running as a generator. (Xote that this 
E. M. F. must be the total E. M. F. produced, calculated for a 
shunt generator from E = e + C a r a , or E = e -\- (C -\- C s )r a .) 
Measure the speed. If it is not the same as that for which E was 
calculated, adjust R 2 until the proper speed is obtained. 

When running at the proper speed and the voltmeter shows the 
proper E. M. F. read A, and call it C A . 

The calculation of losses is as follows, the data known from run- 
ning as a generator being e 3 C. r a , n- : 

O a = ~f » 

E—e+ (C+C s )r a , 

c a = c + c s . 

Loss in armature = C 2 a r a , 

" shunt = C 2 s )'s , 

11 driving = E X Ca. 
Total losses = C 2 a r a + C 2 s r s + EC a. 

Output = eC, 

Input = eC + C 2 a r a + C 2 s r s + EC A . 

eC 
•"• Efficienc ^ =eC + C\r a + C* s r s + EC. ' 

This method is applicable to shunt, series or compound generators, 



482 Naval Electricians' Text Book 

the only difference being in the calculation of the losses in the 
armature and field, as the current flowing in them will be different 
in each class of machine. 

This indirect method can best be illustrated by an example. 

A short-shunt compound generator maintains a difference of 
potential at the terminals of 150 volts at a certain . speed and sup- 
plies 20 amperes to the external circuit. The resistances are 

Armature, .18 ohm, 

Series winding, .07 ohm, 
Shunt winding, .95 ohm. 

Solution: The fall of potential in the series winding = 20 
X .07 = 1.4 volts; therefore, the difference of potential at arma- 
ture terminals = 150 + 1.4 = 151.4 volts. 

Shunt current = — ~^- = 1.59 amperes, 
yo 

Armature current = 20 + 1.59 = 21.59 amperes. 

The fall of potential through armature = 21.59 X .18 = 3.9 
volts. 

When this machine was connected to run as a motor as in Fig. 
219, it was found, when running at the same speed as before, that 
to produce the total E. M. F. 150 ;+ 3.9 = 153.9 volts it required 
.75 ampere. 



Loss in armature 


= 21.59 2 X -18 = 84.8 watts. 


" shunt 


= 1.59 2 X 95 = 240.3 " 


" series 


= 20 2 X .07 = 28.0 " 


Other losses 


= 153.9 X-754= 116.0 " 


Total losses 


— 469.1 " 


Output 


= 20 X 150 = 3000 " 


Input 


= 3469.1 " 


Efficiency 


= !£= 86.4 per cent. 



Commercial Efficiency of Motors. — The commercial efficiency of 
a motor is the ratio of the mechanical power of the motor to the 
electrical power supplied to it, both amounts of power being ex- 
pressed in the same units. 



Experiments with Dynamo Electric Machines 483 

The electrical power supplied to the motor is expressed in watts 
and is found from the readings of a voltmeter and ammeter properly 
connected to the supplying circuit. 

The mechanical power is usually expressed in terms of horse- 
power, one horsepower being 33,000 foot-pounds per minute or equal 
to 746 watts. 

The ordinary mechanical means of measuring the power given 
out by a motor is by some form of brake, or by dynamometer. 

Brakes. — Brakes may be of several kinds, the ordinary ones being 
the band brake and arm brake. 

In the band type, the brake is applied directly to a rotating pul- 
ley on the motor armature shaft, the pull exerted by the brake being 
on the surface of the pulley and tangential to it. 

In the arm brake, the brake is connected to an arm and the pull 
is exerted at the end of the arm, the brake itself being on the sur- 
face of the pulley. 

Formula for Brake Horsepower. — Power is the rate of doing 
work, or the rate of overcoming a force in a given distance. 

In the case of a brake, the force overcome is that exerted at the 
surface of the pulley, due to the turning force of the motor, and is 
overcome by the friction between the brake and the pulley. 

Let / = force in pounds exerted by the brake, 
d = diameter of pulley in feet, 
n = number of revolutions per minute. 

The distance per minute is ird feet, and the work done in n revo- 
lutions is frnrd foot-pounds, and the power exerted is qq'ooo norse " 
power. 

If the arm brake is used, the force exerted by the brake at the 
end of the arm is fl, where I equals the length of arm in feet; and 

the horsepower is 38^. 

Dynamometers. — In all types of brakes, in order to measure the 
power given out, it is absorbed, but this absorption is not necessary, 
if some means is provided of measuring the torque. 



484 



Naval Electricians' Text Book 



The torque is the force exerted at the rim of a pulley on the 
motor shaft and measures its tendency to turn round its axis. 
Numerically it is equal to the force X the radius of the pulley. 
The power given out is the product of the torque and speed. The 
speed is 2-rm feet per minute and the power is 

fr2irn or fdnir foot-pounds. 

Dynamometers are contrivances for measuring torque and are of 
two general kinds, transmission and absorption dynamometers. 




Fig. 220. — Brackett's Cradle Dynamometer. 



Brackett's Cradle. — This form of absorption dynamometer is 
shown in Fig. 220. 

The motor is bolted to a small platform which is suspended on a 
pair of knife edges fixed in a frame, one at each end of the cradle 
in line with the center of the motor shaft when the latter is properly 
placed. The cradle has a swinging motion about the axis of the 
knife edges but is otherwise rigid. 

The cradle is fitted with lugs to which may be secured a gradu- 
ated arm, on which slide known weights. On the cradle are 



Experiments with Dynamo Electric Machines 485 

upright screws on which work different weights, fitting eccentrically 
on the screw shafts, and by these, the center of gravity of the system 
may be made to coincide with the axis of suspension, and the cradle 
can be accurately balanced. 

If necessary a belt or cord may be passed around the motor pul- 
ley and drawn taut, so as to produce a braking effect to reduce the 
revolutions, but without tending to disturb the balance on the 
knife edges. 

Measuring the Output. — When the motor is accurately balanced 
with the weight at the zero of the scale, current may be supplied 
to the motor. The field will tend to rotate relative to the armature, 
due to the drag on the armature conductors, and this drag will pull 
the motor around. It can be brought back to its level position by 
moving the weight out on the arm, or different weights may be 
used at different distances to produce the balance. 

The torque is equal to the product of the weight and the distance 
it is from the center of the shaft, or in case more than one weight 
is used, it is the sum of the products of each weight by its own 
distance. 

As shown above the power exerted, or given out by the motor is 

fdn-K , 
33^ horsepower, 

where / = weight on the arm in pounds, 

d = distance of weight from center in feet, 
n — revolutions of armature per minute. 

It is not necessary that the weight shall be at zero when the motor 
is balanced, but it should be noted where it is, and then knowing the 
distance it has to be moved to obtain a balance, the torque is the 
product of the weight and the distance it has been moved. 

It is also not necessary that the zero of the scale should coincide 
with the center of the shaft, for when the first balance is effected, 
the moment of the weight about the center is counterbalanced by 
the adjusting weights, so the zero mark of the scale can be placed 
at any convenient place on the arm. 



486 Naval Electricians' Text Book 

Determination of Losses. 

In the preceding remarks regarding efficiency, it was shown that 
the difference between the input and output of dynamo electric 
machines was due to the losses in the machine; and expressed as 
watts, the loss is equal to the input minus the output, both of course 
being expressed in watts. 

The losses are of two distinct classes ; those due to the heat pro- 
duced in the armature and field windings, produced by the cur- 
rents flowing through the resistances; and the others due to the 
heat produced by eddy currents in the iron core of the armature, 
the hysteresis loss in the same, and the heat caused by friction in 
the bearings, by the brushes, air friction, etc. The first of these 
are generally referred to as copper losses and are easily calculated, 
the others are called iron and friction losses. 

The separation of these losses is of greatest importance to the 
designer, and tells him how best to reduce the total loss. Exces- 
sive hysteresis shows inferior quality of iron in the armature core, 
and large eddy currents shows poor lamination in the core. Large 
friction losses show inferior lubrication, and possibly improper 
contact of brushes. 

The separation of the iron and friction losses is given here for 
purposes of experiment, as such work is of great help in procuring 
a sound understanding of the entire principles governing the con- 
struction of electric machines. 

Determination of Iron and Friction Losses. — For this experiment 
make connections as shown in Fig. 219 with the addition of an 
ammeter in the field circuit, the machine under test to be run as a 
motor without load. When this is the case there are no copper 
losses, except the extremely small loss due to the current necessary 
to drive the armature, which may be neglected as being less than 
one watt, and all the losses are those due to iron and friction. 

The experiment is similar to that for finding the efficiency of a 
generator (the indirect method) but more observations are taken. 

Instructions. — Eun the machine for some time (one or two 
hours) to get everything running smoothly and conductors warmed 
to a normal extent. 






Experiments with Dynamo Electric Machines 487 



Excite the field to its normal extent, that is by the same current 
it would have when running at normal speed as a generator. By 
means of the adjustable resistance R ± (Fig. 219) get a small volt- 
age at the armature terminals, and with the exciting current con- 
stant, take readings of the armature voltage, armature current 
and speed. 

Always keeping the exciting current constant, increase the arma- 
ture voltage, then make same readings as before. Do this for 
gradually increased voltage till the full voltage is obtained. 



1000 




20 40 60 80 100 120 140 160 180 200 VOLTS 



100 200 300 400 500 600 700 800 900 1000 R.P.M. 

Fig. 221. — Curves Showing Separation of Losses. 



Construction. — With the two variable quantities, armature volt- 
age and armature current, plot points to some convenient scale, 
making volts as abscissae and amperes as ordinates and draw a 
curve through the points so determined. 

Such a curve is shown in Fig. 221 marked C 1 . 

As the armature current is directly proportional to the voltage 
at the terminals, the relation between the current and voltage is 



488 Naval Electricians' Text Book 

constant and therefore the equation to the curve is of the form 
y = mx -f- c, c heing the distance the line starts above the axis 
of volts. 

Since the speed and voltage are proportional with a constant 
excitation, a scale of revolutions per minute may be added. In 
the example assumed 1000 revolutions per minute correspond to 
200 volts. 

The iron and friction loss, or no-load loss curve can now be 
plotted. This is done by plotting the volts as abscissa? and the 
product of volts and amperes as ordinates, a scale of watts being 
marked to a convenient scale on the left. Thus for volts equal to 
40, the current is 3.5 amperes, and the watts 40 X 3.5 = 140. 
This is plotted with 40 as abscissa and 140 as ordinate. Similarly 
other points on the curve are plotted and the curve W t drawn 
through them. 

The ordinates of this curve for any speed will show the " no- 
load " loss at that speed. 

Determination of Friction Losses. — The loss due to friction of the 
brushes and of the bearings increases in direct proportion to the 
speed of the armature, while the air-friction loss varies almost as 
the square of the speed. 

If the armature could be run without any field, there would be 
no iron losses, and the only loss would be that due to friction, so 
the method employed to determine the friction loss is to estimate 
the power required to run the armature without field. 

By observing the current and voltage necessary to keep the speed 
constant, a curve of watts can be plotted to show the no-load loss 
over a considerable range of field excitation. These curves can be 
plotted for different speeds and then an estimate can be made of 
what the losses for different speeds would be if the field excitation 
was zero, which would be the reading of the watts for zero voltage ; 
found by prolonging the curves for the speeds until they cut the 
axis of watts. 

A set of these curves are shown in Fig. 222 in which the same 
scale is used as in Fig. 221, but are plotted separately to avoid 
confusion. 

The data for these curves is found by using the same connections 






Experiments with Dynamo Electric Machines 489 

as in the previous experiment and shown in Fig. 219. The excita- 
tion of the field is varied by the resistance R 2 and the armature 
voltage is adjusted to maintain the speed constant by adjusting E x . 
For the given speed tafce reading of the exciting current, armature 
volts and amperes. Eeduce the exciting current, keeping the speed 
constant by B x and take readings as before. Eepeat this operation 
for the constant speed, reducing the exciting current to as low 
value as can be employed. 



1000 




40 60 

Fig. 222. 



80 100 120 140 160 

-Curves of No-Load Loss. 



180 200 VOLTS 



With a new speed, repeat the operation, getting as many points 
on the curve as possible, especially with the low exciting current. 

For each set of observations, one set for each speed, find the watt 
curve or the product of armature volts and amperes, and with the 
volts as abscissae and watts as ordinates, plot a series of points for 
each speed, and through these points draw fair curves. 

The ordinates of these curves for any armature voltage will give 
the " no-load " loss for the different speeds. 



490 Naval Electricians' Text Book 

These curves are continued until they cut the axis of watts at 
zero voltage, in which case the ordinates at zero voltage will give 
the friction losses for those speeds. 

Eemembering that the curve W t (Fig. 221) represents the total 
no-load loss, the friction losses found from the curves on Fig. 222 
can be transferred to it, and subtracting the friction losses from 
the total loss for the corresponding speed, the remainder will be 
the total iron losses. This will give curve W 2 , the ordinates inter- 
cepted between curves W t and W 2 being the friction losses for the 
different speeds or different armature voltage. 

From curve W 2 , which is the watt curve of iron losses, the cur- 
rent curve C 2 can be plotted by dividing each ordinate (watts) by 
the corresponding abscissae (volts), using for points on the curve, 
volts for abscissae and amperes for ordinates. This curve will be 
a straight line for the same reason as given for curve C x . 

Where the curve C 2 cuts the axis of watts, draw a horizontal 
line C s . This line divides the ordinates of the current line C 2 
into two parts, the portion below the horizontal line representing 
the current required to overcome the hysteresis loss, and the portion 
intercepted between the horizontal line and curve C 2 , the current 
required to overcome eddy-current losses. 

The area of the triangle ABC = \ BC X AC, 

BC 

— — -,= tan a, . ' . area = ^ AC 2 tan a, 

and is therefore proportional to the square of the voltage and conse- 
quently to the square of the speed. Since eddy losses increase in 
proportion to the square of the speed, the area must represent the 
power necessary to overcome them. The area AC ED is propor- 
tional to BE, .'.to the voltage and to the speed, and as hysteresis 
is proportional to speed, this area represents the power necessary 
to overcome the hysteresis loss. 

From the last curve C z , find the watts spent in overcoming 
hysteresis, by multiplying the current ordinate by any voltage 
within the limits of experiment, and drawing a straight line 
through this point to the origin. 

The losses are now completely separated and are as shown in 
Fig. 221. The friction losses are represented by the ordinates for 



Experiments with Dynamo Eiectric Machines 491 

any voltage (or speed) between the two curves W ± and W 2 ; the 
edd} T -current loss by the ordinates between W 2 and W 3 and the 
hvsteresis loss by the ordinates between W s and volt line, and the 
snm of conrse equals the total friction and iron loss for any voltage. 

Example. 

The foregoing separation of losses may be made clearer by an ex- 
ample with assumed values to illustrate the experiment, the values 
taken being those used to plot figure 221. 

In the first part of the experiment, keeping the exciting current 
constant and varying the voltage, the following values were obtained 
in columns I and II. 



I. 

V (volts). 
40 


II. 

C (amperes). 
3.5 


III. 
VC (watts). 
40 X 3.5 = 140 


80 


3.7 


80 X 3.7 = 296 


120 


3.9 


120 X 3.9 = 468 


160 


4.1 


160 X 4.1 = 656 


180 


4.3 


180 X 4.3 = 860 



Curve C x was plotted with the values given in columns I and II, 
and curve W ± with values in columns I and III. 

In the second part of the experiment, the friction loss, the fol- 
lowing data was obtained by keeping the speed constant for a series 
of readings and observing the armature volts and amperes, the 
observed data being given in the second and third columns of the 
four tables, A, B, C and D. 



I. 

Revs. 
900 


II. 
V. 

160 


III. 

C. 
3.6 


IV. 
VC. 
576 


r ■■ 
I. 

Revs. 
700 


II. 

V. 

160 


III. 
C. 

3.6 


IV. 

VC. 
576 


900 


120 


3.8 


456 


700 


120 


3.6 


432 


900 


80 


4.5 


360 


700 


80 


4.2 


336 


900 


40 


7.5 


300 


700 


40 


6.5 


260 


I. 

Revs. 

500 


C 
II. 
V. 

120 


III. 
C. 
3.3 


IV. 
VC. 

396 


r 
I. 

Revs. 

300 


D 
II. III. 
V. C. 

80 2.6 


IV. 
VC. 
208 


500 


80 


3.1 


248 


300 


40 


3.0 


120 


500 


40 


4.5 


180 











The four curves of Fig. 222 were plotted from the data of 
columns II and IV. 



49*2 Naval Electricians' Text Book 

These curves were then prolonged until they cut the vertical axis, 
the orclinates of which gives the friction loss in watts. These values 
are from the curves : 

Revs. Friction watts. 
900 270 

700 210 

500 150 

300 90 

To Plot Curve W 2 . — On ordinate corresponding to speed of 900 
revolutions subtract the friction loss for that speed, thus 

For 900 revolutions (180 volts) 755 — 270 = 485 
700 " (140 " ) 560 — 210 = 350 

500 " (100 " ) 380 — 150 = 230 

300 " (60 " ) 215— 90 = 125 

With the values in the last column of the above table and volts 
corresponding to the speed of the first column, plot curve W 2 . 

To Plot Curve C 2 . — Divide the values in the last column of the 
above table by the voltage corresponding to the speed, thus 

VC. V. c. 

485 -•- 180 = 2.7 
350 -f- 140 = 2.5 
230 ^ 100 = 2.3 
125 -f- 60 = 2.1 

With the values of 7 and C of the above table, plot curve C 2 . 
This will be a straight line parallel to C t for the differences of their 
ordinates is a constant quantity; thus ordinate of C t corresponding 
to 180 is 4.2, to 140 is 4.0, to 100 is 3.8 and 60 is 3.6. The differ- 
ences of the ordinates is then 

4.2 — 2.7 = 1.5 
4.0 — 2.5 = 1.5 
3.8 — 2.3 = 1.5 
3.6 — 2.1 = 1.5 

To Plot Curve C 3 . — This has already been explained. 






Experiments with Dyxamo Electric Machines 493 

To Plot Curve W 3 . — The ordinate of C 3 is the difference be- 
tween that of C x for zero voltage and the differences of the ordi- 
nates of C ± and C 2 , or 3.3 — 1.5 = 1.8 amperes. 
For 20 volts then the watts are equal to 

20 X 1.8 amperes = 36 watts, 
and 40 X 1.8 " = 72 " 
" 60 X 1.8 " = 108 " 
" 80 X 1.8 " = 144 " 
" 100 X 1.8 " = 180 " etc. 
As there is a constant difference the line is straight and can he 
determined by taking any convenient voltage, finding the watts, 
and plotting the point with volts and watts and drawing a straight 
line to the origin. 




Fig. 223. — Exploring E. M. F. Around Armature. 



Determination of E. M. F. Around Armature. 

The object of this test or experiment is to show the distribution 
of potential differences around the armature. If the difference of 
potential is measured between the negative brush and successive 
bars of the commutator it will be found that in a well-designed 
machine the difference of potential increases regularly, though not 
equally, in both directions, becoming a maximum when the position 
of the positive brush is reached. In badly-designed machines the 
distribution will be found to be irregular. 



494 



Naval Electricians' Text Book 



One way of attaining the differences of potential is to measure 
the voltage induced in the coils connected between individual pairs 
of commutator segments at different points around the circum- 
ference. There are two methods in general use of making these 
measurements, depending on the relative position of the individual 
pairs of commutator segments to which the measuring instrument 
is connected. 

Two-Brush Method— S. P. Thompson Method.— If the difference 
of potential between successive segments is required the simplest 
method is to use two small brushes insulated from each other and 
fixed apart a distance equal to that between successive commutator 




2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17 18 

Fig. 224.— Curve of Total Difference of Potential. 



segments, the brushes connected to a low-reading voltmeter. The 
connections are shown in Fig. 223. 

By moving the small auxiliary brushes B around the commutator 
the difference of potential is measured on the voltmeter V between 
any two successive segments on which the brushes make contact. 

The results may be plotted in the form of a curve which will 
show the total difference of potential between brushes or between 
one brush and any particular segment as well as the difference of 
potential between successive segments. Such a curve is shown in 
Fig. 224. 

In Fig. 224 the position of the negative brush is shown at 1 and 
the positive brush at 10, and the commutator segments are num- 
bered consecutively from 1 to 18. If the exploring brushes are 
pressed against segments 1 and 2, the resulting E. M. F. would be 



Experiments with Dynamo Electric Machines 495 

plotted, according to some convenient scale, as an ordinate equal 
to 2 — A. If connected to 2 and 3, the resulting E. M. F. is 
plotted as 3' — B. To this must be added that due to 1 — 2, 
which is 3 — 3'. In other words, following consecutively around 
the commutator, the resulting E. M. E. should be added to the total 
E. M. F. up to that point, and in this way the whole curve is con- 
structed ; after leaving the positive brush, the resulting differences 
of potential will be subtractive from the preceding one. 

Single-Brush Method — Mordey's Method. — A more general 
method of attaining the same result is to use only the auxiliary 
contact brush, to which the terminal of the voltmeter is connected, 
the other terminal being connected to one of the main brushes of 
the machine. By moving the auxiliary brush from one segment to 
another, the difference of potential is measured from the machine 
brush to the segment, and to obtain the difference between any two 
segments it is only necessary to subtract the differences of potential 
between the main and auxiliary brushes, when the latter is con- 
nected to consecutive segments. 

In using two auxiliary brushes, the voltmeter may be a low- 
reading one, as the greatest difference of potential is only that 
between two successive coils, but the single-brush method requires 
a voltmeter to register the complete voltage of the armature. 

The results obtained by the single-brush method can be plotted 
in a curve exactly similar to that shown in Fig. 224. When the 
auxiliary brush is connected to segment 2 the resulting voltage can 
be plotted as A — 2 ; when on segment 3 as 3 — B, etc. 

To obtain the difference between any two consecutive segments, or 
in fact, any two segments, it is only necessary to subtract the ordi- 
nates corresponding to the segments desired. 

Practical Arrangement of a Single-Brush Method — Joubert's 
Method. — A practical method devised by Joubert for examining 
the E. M. F. induced at successive points on the commutator is 
shown in Fig. 225. 

D and E are two wooden discs fitted around the armature shaft 
and can be secured in any position relative to each other. One of 
these is fixed to the shaft and the other is carried by it. The disc 
E is fitted with a continuous metal rim to which is connected a 



496 



Naval Electricians' Text Book 



small spring F which presses against the commutator. Let into the 
rim of B is a contact plate C which has a small tongue which is in 
contact with the metal rim of E. The auxiliary brush B is fixed 
and rubs against the rim of D, making contact with once in each 
revolution. 

When C passes under the brush B, the circuit is completed 
through the voltmeter V. By shifting D and E relatively to each 
other, C and F are brought relatively nearer together or further 
apart, so connection can be made between any two segments of the 
commutator. This device can be so arranged that when is pass- 



K3- {] 




Fig. 225. — Illustrating Joubert's Method of Exploring E. M. F. 



ing under B, F makes contact with the adjoining segment to that 
under the main brush of the machine, so the voltage obtained will 
be that between the main brush and its adjoining segment. By 
shifting F ahead the angular distance of one segment at a time, 
the voltages will be measured consecutively around the commutator 
from the common brush. 

Owing to the fact that the contact of the brush B with the con- 
tact piece C is momentary and intermittent, an ordinary voltmeter 
would oscillate rapidly, or if it was absolutely dead beat, it would 
indicate a mean lower voltage than that corresponding to the voltage 
at the instant of contact. For accurate results, it is better to use 



Experiments with Dynamo Electric Machines 



49-' 



an electrostatic voltmeter with a condenser connected in parallel, 
as the voltmeter would probably have so small a capacity that it 
would discharge itself too rapidly to affect the slow-moving needle. 
A hot-wire voltmeter specially calibrated can be used to good 
advantage. 

In making the test, it is well to connect another voltmeter to the 
machine terminals, and by means of a regulator in the shunt field, 
keep the voltage of the machine constant during the test. 

One experiment can be made with no load on the machine and 
another with full load, and the differences in the resulting curves 




Pig. 226. — Fall of Potential Around Armature. 



of E. M. F. will show the effect of the armature current on the 
field distribution. 

Fall of Potential Around a Stationary Armature. — In the above 
methods, the fall of potential around the commutator has been 
measured by the current produced by the armature itself, but to 
test the similarity of windings in the different sections of an 
armature, an outside source of current can be used and the fall 
of potential due to the resistance of the armature windings can 
be tested. 

Connections are made as in Fig. 226. 

The brushes of the stationarv armature D are connected to an 



498 Naval Electricians' Text Book 

outside source of current and a strong current is sent through the 
armature and a voltmeter V connected to the brushes will show the 
total fall of potential through the armature windings. Another 
voltmeter V is shown connected one terminal to one brush, the 
other to any segment of the commutator. 

If the armature is sound and the windings similar there should 
be the same fall of potential from the leading-in point to segments 
each side equally distant from it, and the fall of potential should 
be the same from one segment to another. If it is not, it indicates 
a fault of some kind in the winding, and this method can be used to 
locate short circuits, as a short-circuited coil would show no change 
of difference of potential from its adjoining coil. 



CHAPTEE XXII. 
MOTIVE POWER FOR GENERATORS. 

The only motive power that has been used on board ships of the 
navy for driving electric generators is steam, with the exception of 
that for motor generators, which is, of course, electric power. 
Experiments were made at one time with water motors as a source 
of power for generator driving, and although good results were 
obtained it never was adopted or tried under service conditions. 

Steam Installation. — The installation of the steam power for 
driving electric generators is usually separate and distinct from all 
other steam-driven machines. Steam pipes are lead direct from 
certain boilers, or all of them, and at each boiler there is fitted a 
separate boiler stop valve, so boilers not in use may be entirely cut 
off. The steam pipes from the boilers lead to a common steam pipe 
at which they are fitted with stop valves. This common pipe is 
generally connected with the auxiliary steam pipe system of the 
ship, but steam from this system is not used if it can be avoided, 
it being generally preferable to use steam direct from the working- 
boilers. 

The common steam pipe enters the dynamo-room, where the steam 
passes through a reducing valve to reduce the boiler pressure to that 
of the working pressure of the generator engines. From there it 
passes through a steam separator, in which any water is separated 
from the steam, and from the separator, branch pipes controlled 
by stop valves lead to each engine. In ships having dynamo-rooms 
on different decks, it is usual to install the reducing valve and 
separator on the lower deck, in which case steam riser pipes lead to 
the upper rooms, although each room may be fitted with its own 
reducer and separator. At the engine the steam is controlled by a 
steam stop valve and in addition a throttle valve. In a compound 



500 Naval Electricians' Text Book 

engine, after passing the throttle valve, steam enters the high- 
pressure steam chest, where it is controlled by the high-pressure 
steam valve, usually of the piston type. Steam enters the high- 
pressure cylinder where the first stage of the expansion is carried 
out, and when the pressure has somewhat fallen owing to the expan- 
sion and work that has been done, it is exhausted into an inter- 
mediate receiver and from there passes into the low-pressure valve 
chest, where it is controlled by the low-pressure valve, usually of the 
slide type. After passing this valve the steam passes into the low- 
pressure cylinder, where it acts on the low-pressure piston and the 
second stage of the expansion is carried out. After it has done its 
work on the piston and the pressure has fallen, it is exhausted 
through an exhaust pipe, controlled by an exhaust valve at the 
engine, and the steam now fallen to the pressure in the exhaust line 
is carried to an auxiliary condenser where it is condensed to the 
form of water. The condensed steam in the form of water is now 
returned to the boiler by feed pumps which draw the water from 
the hot well, to which it has been drawn by the air pump by which 
the vacuum in the condenser is maintained. The object of the 
condenser is to save the water and the heat in the exhaust steam, 
and the air pump is to reduce the pressure against which the steam 
acts in the cylinders of the engine and to remove the condensed 
steam from the condenser. 

The dynamo exhaust line may be connected to an auxiliary ex- 
haust line, but this should not be used except when necessary, as 
the vacuum is generally poor, owing to its long length of pipe and 
numerous joints in which leaks may occur. The connection to any 
exhaust line except the main or auxiliary condensers may lead to 
back pressures which seriously affect the speed of the engines. 

The exhaust line is also fitted to exhaust into the atmosphere if 
for any cause the condensers cannot be used, as when in dry-dock. 

The path of steam from the boiler through the generator engine 
and back to the boiler is shown in Plate I. Ordinarily the con- 
denser with its fittings and pumps is not installed in the dynamo- 
room as shown, but in the engine-room to which the exhaust pipe 
leads. 




3dld 3dV0S3 OX 



502 Naval Electricians' Text Book 

Early Types of Engines. 

The first generators installed on shipboard were driven by belts 
from horizontal engines, bnt the disadvantages of belt driving were 
so very evident that it was only tried on one or two vessels. Since 
then, the generating sets have been directly driven; that is, the 
power of the engine is directly conveyed to the generator shaft, 
either by means of a common shaft for engine and generator or by 
independent shafts connected directly by clutch bearings. 

The first few directly-connected engines were horizontal, direct- 
acting, these being used with the generator known as the Marine 
Dynamo, which combination did not long find favor. 

Following these was the adoption of the general design of engine 
which was the standard for several years, and which may still be 
found in service. This type was simple, single-acting, vertical, 
inverted, two-cylinder. The valves were of the piston type, and 
the arrangement of valves and cylinders in reference to each other 
and to the governor constituted the differences between the various 
designs of this same type. 

Engine Specifications. 

Steam engines for generator driving are built under specifica- 
tions prepared by the Bureau of Equipment, Navy Department, and 
those in force at present are as follows: 

1. Engines are to be of the automatic cut-off vertical inclosed type, 
designed to run condensing with maximum practical efficiency at all 
loads, but capable of satisfactory operation when running noncondens- 
ing, to be of sufficient indicated horsepower to drive the generator for 
an extended time at the rated speed, when said generator is carrying 
a one-third overload. 

2. Sizes 2% K. W., 5 K. W. and 8 K. W., to be simple engine, single 
or twin cylinder at the option of the contractor. Sizes of 16 K. W. 
and above to be cross-compound with cranks set at 180°. 

3. The normal steam pressure under which the engine, running con- 
densing with 25-inch vacuum, for different size sets, is to operate, and 
the maximum allowable water consumption per K.-W. hour output of 
the set are: 



formal steam, 
pressure. 


Water consumption 

per K.-W. hour, 

full load. 


100 




105 


100 




90 


100 




70 


100 




44 


100 




41 


100 




39 


150 




35 


150 




31 



Motive Power for Generators 503 



k. w. 

2.5 

5 

8 
16 
24 
32 
50 
100 

Water consumption to be based on running without lubrication in 
the steam spaces. A lubricant may, however, be used in the steam 
spaces, prior to delivery for the test, when surfacing the bearings in 
the steam spaces. 

In testing, corrections shall be made by calorimeter for entrained 
moisture. Superheating shall not be used in the test. 

4. Engines to run smoothly and furnish the required power for 
full load at any steam pressure within 20$ (above or below) of those 
given in the table, and exhausting to condenser at 25 inches of vacuum; 
to furnish power for 90$ of full load at steam pressure 20$ below 
normal, and for full load at any steam pressure between normal and 
20# above normal, when exhausting into the atmosphere. 

5. To be so designed that the work done by each cylinder, as shown 
by indicator cards, will be as nearly equal as practicable under all 
conditions of load. Indicator motions must be provided which will 
accurately reproduce the motion of the pistons at all points of the 
stroke. This will require, for cross-compound engines, the operation 
of the reducing motion for each cylinder from the cross-head or other 
moving part belonging to that cylinder. 

6. Indicator piping to be installed in a manner to secure accuracy of 
indicator cards. Connections to be made at each end of each cylinder, 
and piped to a three-way cock in order that one indicator may be used 
for both head and crank ends of cylinder. Connections are to fit the 
standard indicators of the Bureau of Equipment. 

7. The length of stroke of the engine to be not less than the diameter 
of the bore of the high-pressure cylinder. 

8. The cylinders to be made of hard, close-grained charcoal iron, 
bored and planed true, steam and exhaust ports to be short, of ample 
area and free from fins, scales, sand, etc. Cylinders for sizes 50 K. W. and 
100 K. W. will be fitted with a bushing for each piston and piston valve. 
Bushings to be securely held in place and of sufficient thickness for 
operation after reboring to a diameter increased by one-quarter inch. 
Cylinders to be fitted with the usual drain piping, check valves, cocks, 



50-4 Naval Electricians' Text Book 

all drains to end in one outlet. In addition to these drains, relief 
valves are to be fitted to each end of each cylinder, and both high- 
pressure and low-pressure valves are to be free to lift from their seats 
to relieve the cylinder of water. 

9. The low-pressure cylinder must be fitted with a flat, balanced 
slide valve; a piston-valve on the low-pressure cylinder will not be 
accepted. 

10. The pistons to be of cast iron or steel, strongly ribbed, light and 
rigid, and fitted with self-adjusting phosphor-bronze rings, with diago- 
nal lap, each piston to have two or more rings. Rings to override 
counterbore of cylinders, to prevent wear to a shoulder. The piston 
and rod to run true at all speeds and to be fitted with such guides or 
tail rods as are necessary to prevent injurious vibrations. 

11. Piston-rods to be of forged steel securely fastened to piston and 
cross-heads. Cross-heads to be of steel with adjustable shoes. Con- 
necting rods to be of steel with removable babbitt-lined or bronze boxes 
for crank-pins and bronze boxes for cross-head pins. 

12. The crank-shaft to be forged in one piece; counterweights for 
balancing reciprocating parts to be forged with it or securely fastened 
thereto. Valve-rods, eccentric rods, and rocker shafts, as well as all 
finished bolts, nuts, etc., to be of best forged steel. 

13. Lagging shall be fitted as extensively as practicable to cylinders, 
receivers, and steam chests. This shall be done after a preliminary 
run of the engine in order that any defects in castings or joints may be 
readily found. The arrangement for securing the lagging in place shall 
admit of its ready removal, repair or replacement. 

14. The steam and exhaust outlets shall be so placed as to admit of 
piping from either side with equal facility. Blank flanges shall be 
furnished complete when required to cover alternative outlets. 

All flanges for steam and exhaust to be in accordance with Bureau of 
Steam Engineering standards. 

All exhaust flanges will be for copper pipes with composition flanges. 

Unless otherwise directed, flanges for steam pipes two inches in 
diameter and larger will be for steel pipes with steel flanges, and 
flanges for pipes less than two inches in diameter will be for copper 
pipes with composition flanges, except when steam is superheated, in 
which case flanges for all steam pipes will be for steel pipes with steel 
flanges. 

15. Throttle and exhaust valves to be furnished with each set and to 
conform in every respect to standard specifications and drawings of the 
Bureau of Steam Engineering. To be 90° angle valves, looking up, 
unless otherwise specified. Handwheels to be marked, indicating direc- 
tion of turning for opening and closing. All throttle valves three inches 
and larger shall be fitted with by-pass valves for warming up cylinders. 



Motive Power for Generators 505 

16. The governor shall be of the inertia type, arranged to operate the 
valve by varying the valve travel and point of cut off; must regulate 
the speed of the engine automatically with throttle wide open within 
the limits prescribed, and no dashpots or friction washers shall be 
used in its construction. 

17. The speed variation must not exceed 2y 2 % when load is varied 
between full load to 20$ of full load, gradually or in one step, engine 
running with normal steam pressure and vacuum. A variation of not 
more than 3^# will be allowed when full load is suddenly thrown on 
or off the generator, with constant steam pressure, either normal or 
20$ above normal; a variation of not more than 3%# will be allowed 
when 90^ of full load is suddenly thrown on or off the generator with 
constant pressure at 20$ below normal; exhaust in both cases to be 
either into condenser or atmosphere. No adjustment of the governor 
or throttle-valve during the test shall be necessary to insure proper 
performance under any of the above conditions. 

18. The engine column to be designed to inclose all moving parts 
as far as practicable, or where weight may be saved, by using a 
wrought-steel frame with an enveloping inclosure of metal. The design 
of the column shall be such that it is not necessary to raise cylinder for 
disassembling set. Detachable hinged doors to be provided for examin- 
ing moving parts while in operation. The design to eliminate all 
chance of oil or water leaking or being forced through. 

19. Stuffing boxes for piston and valve rods to be fitted with self- 
adjusting metallic packing, except the auxiliary or wiper stuffing boxes 
in the guard plate, which will be fitted with soft packing, having a 
lateral bearing surface of length at least equal to the diameter of the 
rod. If desired, bushings may be fitted in guard plate in lieu of 
auxiliary or wiper stuffing boxes. Stuffing boxes for piston rods and 
valve rods to be accessible from the outside of the inclosing case of the 
engine. 

20. A guard plate to be provided to prevent oil from being thrown 
against the lower cylinder heads and valve chests. Guard plate to be 
flanged at outer edge and to contain an oil well, with strainer, pipe 
and valve, for draining water to bilge. The cylinders are to be of 
sufficient height above the guard plate to insure that no part of piston 
rods or valve rods which enter the auxiliary or wiper stuffing boxes 
or bushings in the guard plate will raise to within one-half inch of the 
lower face of the glands of main stuffing boxes. 

21. Engines are required to operate satisfactorily without the use of 
lubricants in the steam spaces, and this will be demonstrated by a forty- 
eight hour test for each type and size of engine. The lubrication for 
all other working surfaces shall be of the most complete character. No 
part shall depend on squirt-can lubrication. 



506 Naval Electricians' Text Book 

22. Forced lubrication shall be used wherever practicable, which in- 
cludes engine shaft, crank-pins, cross-head bearings, eccentric, etc. 
The engine shall be capable of satisfactory operation with a low grade 
of lubricating oil, and the forced lubrication shall not be a necessary- 
factor in its cool and satisfactory running. The intent of the forced 
lubrication is to reduce friction, noise, and attention required. 

The pressure for such forced lubrication shall be approximately 15 
pounds per square inch, and shall be between 10 and 20 pounds under 
all service conditions. An oil gauge will be fitted on the front of the 
set. The main oil-supply pipe to be tapped by a small pipe terminating 
in a petcock outside of casing. The system to be fitted with a relief 
valve discharging into column of engine. When it is difficult to de- 
termine whether or not oil is feeding properly, a sight oil cup or other 
suitable device will be installed. 

23. The bed-plate is to contain a reservoir and cooling chamber of 
ample capacity, to be provided with a strainer which may be removed 
without interrupting the oil supply. The pump to be direct driven by 
a crank or eccentric on the engine shaft, construction to be simple and 
durable, and to include a proper guide or support for the plunger rod. 
The pump to handle clean oil only, not drawing from the top or bottom 
of reservoir. 

To allow inspection while running, the engine crank is not to dip in 
oil in reservoir. 

24. Fly-wheel to be turned on face and sides, inner edge to be flanged 
to retain any oil which may drip thereon. Hub to be split and clamped 
to shaft by through bolts. A steel starting bar or its equivalent to be 
furnished in sizes of 16 K. W. and over, the fly-wheel surface to have 
not less than six holes for starting-bar. 

A starting-bar and set of wrenches and lifting eyes to be furnished 
and to be suitably mounted in tool board. Stowage to be such that 
parts will be securely held in place, yet readily removed and returned. 
When more than one generating set is supplied for one dynamo room, 
the number of tool boards will be as specified. 

25. Mandrels, with collars, complete, shall be furnished for renewing 
white metal of all bearings so fitted. 

26. Metal name-plate to be fitted to engine in a conspicuous place, 
marked as follows: 

Made for 
Bureau of Equipment 

by 
(Name of maker here.) 

Req. No. , 190—, 

Type . Class . Form . 

K. W. . Steam . Rev. . 

Bore, . Stroke, . Rod Diam., . 



Motive Power for Generators 507 

Engines have been designed and constructed to meet the above 
specifications or others in force at the time by the General Electric 
Company, W. D. Forbes & Co., and The B. E. Sturtevant Company. 
In ships built by the Union Iron Works, there have usually been 
installed engines built by the same firm. As all are built under 
the same specifications, they all present the same general character- 
istics, differing in such details that are not specified, as the kinds 
of packing, style of governor, etc. By far the greatest number of 
engines in use have been furnished by the General Electric Com- 
pany, and only those will be considered in any detail. 

Tandem-Compound Type. 

This type of engine, made by the General Electric Company, is 
used with generators of 16, 24, 32 and 50 kilowatts. A cross- 
section of this engine is shown in Fig. 227. 

This design of engine seems to have met every requirement and 
has proven its worth after ten or more years of experience ; the only 
objection being in the head room required, and which has necessi- 
tated the later design of the cross-compound type. 

This type of engine gets its name from the two cylinders being 
in line; the power developed in the cylinders is transmitted to the 
crank-shaft by a single piston-rod which carries both pistons. The 
high-pressure cylinder is the lower and over it is secured the low- 
pressure cylinder. In the engine of the 32-kilowatt size these are 
respectively 9 inches and 15 inches in diameter with a 6-inch 
stroke. 

The steam valves are cast-iron balanced valves. The high-pres- 
sure valve receives its motion from the governor through a rocker 
arm and the low pressure from an eccentric on the shaft. Steam 
is admitted through the throttle valve to the inside of the high- 
pressure valve B; the admission edges marked FF control the time 
of admission of steam to the high-pressure cylinder, and the exhaust 
edges GG control the time of the exhaust from the high-pressure 
cylinder to the receiver D. After the steam has done its work on 
the high-pressure piston and is exhausted into the receiver D, it 
enters the body of the low-pressure valve A which controls the ad- 



508 



Naval Electricians' Text Book 




Fig. 227. — Cross-Section Tandem Compound. 



Motive Power eor Generators 509 

mission of steam to the low-pressure cylinder by the edges II and 
the exhaust by the edges J J. After the second stage of expansion 
in the low-pressure cylinder the steam is finally exhausted into E. 

The travel of the high-pressure valve is controlled by the governor 
and varies between 3 inches and If inches and the cut-off varies 
between § and zero, depending on the load. The cut-off in the low- 
jDressure valve is fixed at § stroke, while the valve has a fixed stroke 
of o-^q inches. The steam lap of the high-pressure valve is f inch, 
the exhaust lap, top and bottom is inch. The steam lap of the 
low-pressure valve is yg- inch, the exhaust lap is top inch, bottom 
xV inch. 

Valve Stems. — Both valves turn freely on the stems without play. 
The lower ends of the stems are threaded and screw into a small 
cross-head to which they are secured by lock-nuts. The central 
portion of this cross-head is square while the ends are cylindrical 
forming bearings by which the cross-head is connected to the link. 
The caps of the bearing are secured by bolts screwed into the bot- 
tom of the link bearing surface and locked by a nut. "Wear in the 
bearing caps is taken up by filing the face of the caps. 

Pistons. — The low-pressure piston is of cast iron with a single 
rectangular groove which receives the piston packing. The piston 
is screwed on the rod against a taper shoulder and is secured by a 
lock nut in the face of which are radial grooves. A split pin passes 
through the end of the rod and lies in one of the grooves. 

The high-pressure piston is of steel and is screwed to the rod 
and riveted to prevent unscrewing. 

The piston-rod is of forged mild steel, and for the 32-kilowatt 
size is If inches in diameter for the low-pressure section and If 
inches for the high. It is threaded at the lower end for screwing 
into the cross-head, where it is locked by a spanner jam nut. 

The piston packing consists of four cast-iron arcs, overlapping 
at the ends and made steam-tight by brass tongues, one of which is 
riveted to each arc. The packing is held against the cylinder by 
flat steel springs, one to each arc. The packing for the high- 
pressure piston is the same with the exception of three instead of 
four parts. 



510 



Naval Electricians' Text Eook 



Piston-Rod Packings. — There are known as the " Single-Junior " 
type and are shown in Fig. 228. 

Three rings of babbitt metal packing rest on a vibrating cap 
which has a spherical bearing. Over the metallic packing and 
around the rod is a sleeve pressed by a coiled spring. Steam pres- 
sure forces the packing against the rod and the spring prevents the 
packing from following the rod on reversal. 

The cover for the metallic packing in the high-pressure cylinder 
forms a second stuffing-box for two rings of soft packing, which is 




Fig. 228. — Single-Junior Piston-Rod Packings. 



used to prevent water from following the rod and mixing with 
the oil. 

The connecting rod consists of a forged steel body forked at the 
upper end for receiving the wrist-pin brasses. Wear is taken up 
by filing the faces of the brasses. The crank-pin bearing consists 
of a cylindrical cast-steel shell in halves. The interior of the shell 
is babbitted where it bears on the crank-shaft, and wear is taken up 
by removing liners between the halves of the steel shell. The bear- 
ing boxes should be kept tight to prevent leakage of oil which is 
forced from this bearing to the cross-head guide. 



Motive Power for Gexerators 



511 



The crank-shaft with the crank is made from one solid piece of 
forged steel. Cast-iron balance weights are secured on the cranks 
opposite the crank-pin. 

In the coupling between the engine and generator shaft are four 
1-inch bolts, with two f-inch set-screws for separating the two 
parts when the armature is disconnected. 

The main bearings are two in number and are cast-iron cylin- 
drical shells, 8 inches in length. The shells are in two parts ; the 
lower part receives the main bearing boxes and the upper part acts 
as a cover to prevent the throwing of oil. The bearing boxes are 
of cast iron lined with a babbitt metal with a facing next the crank 
of the same material. Wear is taken up by machining off the 
composition liners between the boxes. 

The governor is on the 
shaft on the end farthest from 
the generator and is con- 
tained in a heavy fly-wheel 
made very large and heavy 
which is keyed to the shaft. 
The governing mechanism 
contains a single fry-weight 
connected to the lever carry- 
ing the pin that operates the 
high-pressure valve. A circu- 
lar coiled spring opposes the motion of the fly-weight and by 
increasing or decreasing the tension of this spring the speed may 
be varied. Increasing the tension of the spring decreases the ten- 
dency of the fly-weight to move out and the travel of the valve is 
less readily influenced and the effect is to increase the speed. The 
same effect can be produced by moving the spring in the slot away 
from the fulcrum, as this has a tendency to increase the tension and 
consequently the effect is to increase the speed. 

To Remove Governor Wheel. — The governor wheel must be taken 
off before the crank-shaft can be removed. This is accomplished 
by means of the governor disconnector furnished with the engine 
tools. 

Fig. 229 shows the disconnector in ]}lace for removing the gover- 




Fig. 229. 



512 



Naval Electricians' Text Book 



nor wheel. It is bolted to the wheel on each side of the shaft. A 
nut with recessed head is screwed into the crank end, and the 
bolt B is screwed down through the connector on this nut, thus 
raising the connector on the bolt and the latter withdrawing the 
wheel. 

Fig. 230 shows the disconnector in place for replacing the 
governor wheel. There is a square-headed nut screwed into the 
end of the crank-shaft, and on this bears the bolt G, screwing 
through the disconnector A and being set down by turning the nut 
E. A is bolted to the wheel as before, and screwing down E, 
forces A down, forcing the wheel on the shaft. 

Lubrication. — Engines of the tandem type employ the forced 
system of lubrication. The general system adopted is illustrated in 

Fig. 231. The base of 
the engine forms an oil 
tank to which is attached 
a small plunger pump 
driven by an eccentric on 
the shaft. The lubricant 
is carried under pressure 
to the various parts of 
the engine by the me- 
chanism shown in the 
figure. 

The oil is forced by a pump to a groove in the main bearing, and 
a drilled hole in the shaft connects this groove with the crank-pin. 
From the crank-pin box the oil is further forced to the wrist pin 
through the pipe running along the side of the connecting rod. 
The passage in the cross-head allows the oil to be forced from the 
wrist pin to the guides. 

As the oil is forced from one bearing to another, it is quite im- 
portant that the bearing caps be set tight, otherwise the oil will 
escape before reaching the last bearing. After passing through the 
bearings the oil is collected in the base, strained and used again. 
This system of lubrication is perfectly reliable, prevents hot 
bearings, and reduces the wear to a minimum with the least atten- 
tion. It is important that the oil be free from all substances, such 




Fig. 230. 



Motive Power for Gexerators 



513 



as particles of waste or grit, and to guard against the introduction 
of any foreign matter, a strainer which may be taken out for 
examination or cleaning, is attached to the suction valve of the 
pump. An oil pressure of from 5 to 20 pounds should be main- 
tained, and may be regulated by adjusting the set-screw on the 
relief valve of the oiling system. The pressure gauge need not 
remain in the circuit continuouslv. Only mineral oils should be 




Fig. 231. — Lubricating Mechanism. 



used for lubrication. A heavy oil gives better results and prevents 
knocking more effectively than thin oil. An oil which has been 
found to give good results consists of two-thirds red engine oil and 
one-third heavy cylinder oil. As the oil passes through the bear- 
ing repeatedly, it gradually loses its lubricating properties, becom- 
ing thick and gritty, and should be occasionally run through a 
filter and mixed with new oil. The frequency of this change 
depends upon the oil, as well as the number of hours the engine is 
in operation, and can be easily determined by observation. The 



514 Naval Electricians' Text Book 

oil in the reservoir should stand about 2 inches over the suction 
and discharge valves, and no water should be allowed to mix with it. 
Should any water accumulate in the base it should be drawn off by 
the cock provided for the purpose before starting the engine. 

General Electric Form H-l Engine. 

This form of engine, made by the General Electric Company for 
use with their generators, followed the type of the tandem com- 
pound, and was designed to meet the specification calling for a 
cross-compound engine, which became a necessity on account of the 
head room of the larger sizes of the tandem type. 

The following description of the various parts is taken from the 
Instruction Book furnished by the makers, and for an engine to 
drive an MP-6-24-400-80 generator: 

Engine. — The engine is of the vertical, cross-compound, double- 
acting, enclosed type, with cranks 180° apart, and has a speed of 
400 revolutions per minute at full load, with 100 pounds steam 
pressure and 25-inch vacuum exhaust. 

Part of the heavy base supporting the engine and generator 
forms a reservoir for the oil used in lubricating the moving parts 
of the engine. This chamber is also utilized as a settling and cool- 
ing chamber. The base is provided with a depression around the 
engine column for the collection of waste oil and drippings, and is 
provided with a stopcock for drainage. 

On the back of the engine base is cast a boss to which is attached 
a sight tube oil gauge, for indicating the height of oil in the 
reservoir. 

The crank pit, which is enclosed by the column and base, is 
accessible through doors in the front and back of the engine. 

Steam Pressure. — The range of steam pressure for this engine is 
between 80 and 120 pounds, with a normal pressure of 100 pounds 
and 25-inch vacuum. The engine will carry an overload of 33 J 
per cent without trouble. It is advisable to maintain normal steam 
pressure, if possible. 

Cylinders.— The cylinders are 6J" X 10J" with a stroke of 7 
inches. The high-pressure and low-pressure cylinders, with their 
respective steam chests, are a single casting of hard, close-grained 



Motive Power for Generators 



515 



cast iron, accurately bored and externally covered with a thick 
layer of best quality asbestos, and is lagged with planished sheet 







Fig. 232. — Vertical Section of Engine. Form H-l. Gen. Elec. Co. 



iron. The receiver, of proper dimensions, forming a part of the 
cylinder casting, conveys the exhaust steam from the high-pressure 



51G 



Naval Electricians' Text Book 



cylinder to the low-pressure steam chest and is tapped for a J-inch 
drain pipe. For ease in casting, an opening is formed in the re- 
ceiver, this opening being closed by a cover secured by eight f-inch 
studs and nuts. Both cylinders have relief valves and are tapped 
for drain and indicator valves. The draining arrangement with 
|-inch relief valves and three-way cock for high-pressure cylinder, 

is shown in Fig. 233. The f- 
inch relief valves for the low- 
pressure cylinders are of the same 
construction. The high-pressure 
steam chest cover, the low-pres- 
sure cover with relief plate, and 
high-pressure and low-pressure 
cylinder heads are shown in Fig. 
232, 

The high-pressure cylinder head 
is fastened to the cylinder by 
seven f-inch studs and the low- 
pressure cylinder head by eight 
f-inch studs. The flanges of both 
heads and low-pressure steam 
chest cover are tapped for two 
f-inch eyebolts for use in lifting 
these parts. 

The high-pressure steam chest 
cover and high and low-pressure 
cylinder heads are covered by a 
polished cast-iron hood. 

Steam Distribution and Valves. 
— The steam distribution is ac- 
complishes! through one cast-iron balanced piston- valve A (Fig. 
232) and one flat, partially balanced slide-valve fitted with relief 
ring to reduce friction, and driven by an eccentric fixed on the 
crank-shaft, and, therefore, always gives the same cut-off. The 
inner face of the low-pressure steam chest cover is exactly parallel 
with the valve seat and upon this surface the circular ring of the 
low-pressure valve has its bearing. This ring fits a groove in 




Fig. 233. — Draining Arrangement. 



^Motive Power for Gexerators 



51 



the valve and is held in place by springs and is self-adjusting for 
steam tightness, thus automatically following up all wear and 
affords necessary relief in case of water in the cylinder. 

Timed by the movement of valve A, the steam enters the high- 
pressure cylinder chest and valve in proper quantities through the 
throttle-valve, and after doing its work in the high-pressure cylin- 
der, is exhausted in receiver C, admitted to the low-pressure cylinder 
by valve B, and finally exhausted through passage D. 




Fig. 234. — Cross-Head and Link. 



High-Pressure Valve. — The high-pressure valve takes steam on 
the inside, the admission edges being at E and E, and the exhaust 
edges at F and F. 

The steam lap is-fj inch; the exhaust lap top and bottom is 
inch. The travel of this valve is controlled by the automatic gover- 
nor, and varies between 2^ inches and J inch. The cut-off varies 
between f and 0, depending upon the load. 

Low-Pressure Valve. — The admission edges of the low-pressure 
valve are at G and G, and the exhaust edges at H and H. 

The steam lap is -^f inch, and the travel of the valve 2 J inches, 
giving a cut-off of about 0.58 stroke. The exhaust 'lap is minus 
■^q inch top and bottom. 



518 



Naval Electricians' Text Book 



Valve Stems. — The upper ends of the valve stems pass through 
the valves, the valves being secured by double f-inch nuts on their 
upper sides and by shoulders turned upon the valve stems on their 
lower sides. In addition, the low-pressure valve stem is fitted with 
a washer fitted to a taper on the stem which allows the valve to 
properly adjust itself on the stem. 

The nuts should be locked hard together, but the stems should 
be free to turn in the valves, though without any play. 

The valve stems are threaded at their lower ends, and screw into 
small cross-heads, to which they are secured by lock-nuts. The 
central portions of these cross-heads are square, with their ends 
cylindrical, the high-pressure valve stem cross-head forming a bear- 
ing with link B (Fig. 234). The bearing caps C and C for the 




UL \ZQ.D 



Fig. 235. — Eccentric Rod and Strap. 



valve-stem cross-head are each secured by bolts. The lower end of 
the link of the high-pressure stem contains a bearing similar in 
construction, which receives a fixed pin in the rocker arm. The 
wear is taken up by filing the cap faces. The low-pressure valve 
stem cross-head forms a bearing with brasses secured to the forked 
ends of the eccentric rod. In the square section of this cross-head 
are drilled and tapped, at right angles to the hole receiving the valve 
stem, two holes for receiving the J-inch flat-headed screws which 
secure the two bearing-metal shoes to the cross-head, having a bear- 
ing in the cast-iron guide bolted to the cylinder, which acts as a 
guide for the valve stem. 

Lost motion may be taken up by inserting thin liners between 
the cross-head body and the shoes. 

The guide is shown in Fig. 232, while the cross-head and shoes 
are shown in Fig. 2'35. 



Motive Power for Gexerators 



519 



Valve-Stem Stuffing-Box. — Fig. 232 shows the valve chest bonnet 
with stuffing-box. Ordinary soft packing of good quality may be 
used in this stuffing-box. 

Low-Pressure Eccentric Rod and Strap. — The low-pressure eccen- 
tric rod and strap complete are shown in Fig. 235. The upper end 
of the eccentric rod is forked and receives the brasses of the low- 
pressure valve stem cross-head, its lower end being secured to the 
top half of the strap by two J-inch studs. 

Wear is taken up by filing the bearing faces of A and B. 

The lubrication for the eccentric strap is accomplished by oil 
holes drilled through the eccentric, which communicates with the 
inside of the engine. 




Fig. 236. — Rocker Arm. 



Rocker Arm. — The motion for the high-pressure valve is trans- 
mitted from the governor through the rocker arm, bearing upon 
stud A (Fig. 236), which passes through the engine column. The 
washer B, at the end of the stud A, is tapped for a screw grease 
cup which forces the lubricant to chamber C, in the rocker arm. 
The grease is further pressed from this chamber through pipes D 
and D to pins E and E. 

Governor. — The governor is illustrated in Fig. 237, and consists 
of a heavy fly-wheel A, keyed to the shaft and carrying the gover- 
nor parts, the latter consisting of a single fly-weight B pivoted at 
and containing the eccentric pin D which operates the high-pressure 
valve. 



520 



Naval Electricians' Text Book 



The operation of the governor is as follows : 
The governor connecting rod (Fig. 238) which transmits motion 
from the governor to the high-pressure valve is connected to eccen- 
tric pin D. It is therefore 
evident that the length of the 
valve stroke depends upon the 
distance of D from the cen- 
ter of E. The amount of 
steam admitted to the cylin- 
der varies directly as the dis- 
tance between the centers of 
D and E ; that is, the less the 
distance the less the amount 
of steam admitted, and vice 
versa. 

Suppose the speed of the 




Fig. 237. — Governor. 



engine to increase ; the weight 



o_o 






B is immediately drawn out 
by centrifugal force toward the perimeter A, thus decreasing the 
distance of D from the center of E and reducing the amount of 
steam admitted to the cylinder. Should the speed of 
the engine approach a dangerous point, the distance of 
D from the center of E will be diminished until the 
minimum distance is reached, when the steam is en- 
tirely cut otf from the cylinder. The motion of the 
fly-weight is opposed by the spring F, which is attached 
to the pulley and fly-weight. By increasing or decreas- 
ing the tension of the spring, the speed may be raised 
or lowered. The same effect will be produced by mov- 
ing the spring in the slot of the weight — moving it 
away from the fulcrum increases the speed, and toward 
the center produces the opposite effect. Unstable regu- 
lation may be due to one of two causes — insufficient 
lubrication of the fly-weight fulcrum, or too close an ad- 
justment of speed. The former may be avoided by occa- 
sionally cleaning the governor ; the latter by moving FlG 2 38 
the spring attachment away from the fulcrum. Only Governor 
the best quality of soft grease should be used in the cup. '■ Rod. 




Motive Power eor Generators 



521 



Method of Handling Governor Wheel. — The removal of the 
governor wheel is accomplished by the use of the governor discon- 
necter shown in Figs. 229 and 230. 

Governor Connecting Rod. — The governor connecting rod com- 
plete is shown in Fig. 238. The body A is threaded and screwed 
into the top and bottom of bearing metal boxes B and C, and se- 
cured by lock-nuts. The bearing caps D and E are each secured 
by two f -inch studs with double nuts. 

Wear is taken up by filing the bearing faces of caps D and E. 

The lubrication of the top box is through the rocker arm as 
described under the heading " Eocker Arm " and for the bottom 
box through valve motion lever in the governor. 




(X~) 




Fig. 239. 



Fig. 240. 



Grease Cups. 



Grease Cups. — The different types of grease cups used on this 
engine are shown in Figs. 239 and 240. Fig. 239 shows the auto- 
matic type " Ideal No. 1." The cup is provided with a leather- 
packed plunger, against which rests a coiled spring. The spring 
and the plunger are conveniently controlled by a thumb nut; turn 
this to the right until the plunger is raised to the top of the cup, 
unscrew the cover and fill the cup with grease. Eeplace the cover 
and adjust the pressure on the grease by turning the thumb nut to 
the top of the stem, allowing the spring to press on the plunger, 



522 



Naval Electricians' Text Book 



forcing out the grease. The rate of speed may be regulated by 
the set-screw in the lower part of the cup in which there is a hole 
in line with the slot. 

The " Marine " grease cup No. 1 is used for forcing the lubri- 
cant to the rocker-arm and valve-motion pins. The operation is 
easily understood from the sketch. 

Indicator Motion. — When it is desired to indicate the engine, a 
small cover must be removed from the front column door, exposing 
a slot over which a bracket containing a bearing pin for the lever 
is attached. 




Fig. 241. — Piston, Rod and Cross-Head. 



The indicator motion consists of a stud screwed into the wrist 
pin of the high-pressure connecting rod for driving the motion, 
which connects through a link to a lever pivoted to the bracket cover- 
ing the slot in the door. The motion for the indicator is taken 
from a cord pin on this lever. 

Piston, Rod and Cross-Head. — The piston-rod A and the cross- 
head B (Fig. 241) are in one forging of mild steel. 

The diameter of both high-pressure and low-pressure rods is 
l T 3 g- inches. 



Motive Power for Generators 



523 



The cross-head shoe C is of composition metal, babbitted, and has 
a very liberal wearing surface so that the wear at this point will 
be very slight. The cross-head shoe is fastened to the cross-head 
by two f-ineh bolts and is held against the guide bar by the clamp 
D, which is connected to the shoe by six through bolts. The proper 
distance between the shoe and clamp is maintained by adjustable 
liners E. The cross-head is slotted to receive the wrist-pin bear- 
ing, which is made of gun metal, and is held in jDlaee by cap F and 
two bolts with double nuts. Feathers J inch in diameter and f inch 
long, projecting through the bolt heads and extending into the 
body of the cross-head prevent the bolts from turning. The bear- 
ing should be so adjusted that when the brasses are hard together 
the wrist pin will move freely but without any play. 

Oil reaches the bearing from the oil pipe G (Fig. 243), passing 
up the side of the connecting rod; from this bearing it is further 
forced to stride. 




For Goi/emor 
Disconnector 



/ 
O// Pump 

Eccentr/c 



Fig. 242.— Crank-Shaft and Coupling. 



Pistons and Piston Packing. — The high-pressure piston is shown 
in Fig. 241, and is a cast-iron disk containing two rectangular 
grooves, which receive the piston packing, consisting of a single cast- 
iron spring ring, overlapping at the ends and forming an angle 
joint. The piston fits on a taper on the rod and is secured by a 
nut on the upper side. The outer face of this nut has radial 
grooves cut in it. A split pin passes through the nut, preventing 
it from working loose. 

The general construction of the low-pressure piston is the same 
as that for the high pressure. 

Crank-Shaft and Coupling. — The crank-shaft and coupling (see 
Fig. 242) for transmitting the power to the generator are made in 
one solid piece of forged steel with the crank-pins machined out. 



524 



Naval Electricians' Text Book 



The shaft on one end receives the governor wheel and on the oppo- 
site end the coupling has four J-inch bolts, while two f-inch set- 
screws are used for forcing the coupling apart when it is desired 
to disconnect the armature. 

To the face of the coupling is secured by four J-inch flat-headed 
screws the radial key f-inch square for transmitting the power. 

The shaft has a diameter of 3 inches at the bearing and 2§ inches 
at the governor end. 

Connection Rod. — The connection rod consists of a forged-steel 
body A (Eig. 243) forked at its upper end for receiving the wrist 
pin, which is shrunk into the rod. The bottom end of the rod 
terminates in a stud, to which the crank-pin box is secured by a 
steel cap B and two f-inch forged steel through bolts C, held by lock- 
nuts D. Split pins pass through the ends of these bolts, prevent- 
ing the lock-nuts from coming off. 




6 



irr 



a 



B U 



% 

$ 



Fig. 243. — Connection Rod. 



The crank-pin bearing consists of a hollow, cylindrical, cast- 
steel shell EE, split in halves. The shell has two small flanges 
which fit the connecting rod and prevent the shell from moving 
sideways. It is prevented from turning by the through bolts which 
intersect it and thereby make a guide for it. The interior of the 
shell, which comes in contact with the shaft, is babbitted and wear 
may be taken up by removing the fiber liners F. 

It is important that the boxes should always be tight together in 
order to prevent the oil from leaking out, as the oil must be forced 
from this bearing through pipe G up to the wrist pin and cross-head 
guide. 

Throttle-Valve. — Fig. 244 illustrates the throttle-valve furnished 
with each engine. It is of the Lunkenheimer regrinding type and 



Motive Power for Gexerators 



5.25 



is 2 inches in diameter. When the valve seat becomes worn and 
leaky it may be reground in the following manner: 

Unscrew the bonnet ring and take the valve apart. Place a little 
powdered sand and soap on the disk. Insert a nail or a piece of 
wire in the holes in the disk and stem to prevent the revolving of 
the disk on the stem, and then regrind the valve. The bonnet ring 
should be left unscrewed, so that the bonnet will rotate and guide 
the stem while the valve is being reground. When j>roperly re- 
ground, the valve will again be steam-tight. 

All other valves used on this engine are 
of the same make and construction and, 
therefore, can be reground in the same 
manner. 

Lubrication. — The lubricant is carried 
under pressure to the various parts of the 
engine by the mechanism shown in Fig. 
245. The base of the engine forms an oil 
tank to which is attached a small plunger 
pump driven by an eccentric on the shaft. 
The oil is forced by this pump to grooves 
in the main bearings, and drilled holes in 
the shaft connect these grooves with the 
crank-pins, the oil being further forced to 
the wrist pins through the pipes on the 
side of the connection rods. 

The passages in the cross-heads (see Fig. 241) allow the oil to 
be forced from the wrist pins to the guides. As the oil is forced 
from one bearing to another it is quite important that the bearing 
caps be set tight, otherwise the oil will escape before reaching the 
last bearing. After passing through the bearings the oil is col- 
lected in the base and used over again. 

This system of lubricating is perfectly reliable, prevents hot- 
bearings and reduces wear to a minimum, and necessitates the least 
attention. It is important that the oil be free from all substances 
such as particles of waste or grit, and to guard against the intro- 
duction of any foreign matter a strainer is attached to the suction 
valve of the pump, which may be taken out for examination or 
cleaning at any time whether the engine is in operation or not. 




Throttle-Valve. 



526 



Naval Electricians' Text Book 



A pressure gauge is attached to the system to show the pressure 
of the oil, hut it is not necessary to keep the gauge in circuit 
continuously. 

An oil pressure of from 10 to 20 pounds should be maintained 




0//Pc//r)p EccenCr/'c 



^o^o= 



Fig. 245. — Lubricating Mechanism. 



and may be regulated by adjusting the set-screw of the relief valve 
projecting through the casing on the back of the engine. 

Only mineral oils should be used for lubrication. A heavy oil 
gives better results and prevents knocking more effectively than thin 
oil. An oil which has been found to give good results consists of 
two-thirds red engine oil and one-third heavy cylinder oil. As the 
oil passes through the bearings repeatedly, it gradually loses its 



Motive Power for Generators 527 

lubricating properties, becoming thick and gritty, and should be 
occasionally run through a filter and mixed with new oil. 

The frequency of this change depends upon the oil as well as 
the number of hours the engine is in operation, and can be easily 
determined by observation. 

A small door bolted to the base is utilized when it is found neces- 
sary to clean the reservoir, the oil being first drawn off by a drain 
cock attached to a boss in the front of the engine. 

The oil in the reservoir should stand about 2} inches over the 
suction 'and discharge valves, and no water should be allowed to 
mix with it. 

Starting the Engine. — Before steam is admitted to the cylinders 
care must be taken to see that the valves move freely. This may 
be done by turning the governor wheel by hand. As the expansion 
of the valves is much more rapid than that of the cylinder, the 
cylinder should be allowed to attain its proper temperature before 
full pressure is applied. 

A small pipe J inch in diameter, fitted with a valve, is connected 
between the receiver and the throttle valve. This is for the pur- 
pose of heating the engine before starting. The drain from the 
receiver, together with all the cylinder drain valves, should be kept 
open, to allow all condensed water to escape. 

If water hammering occurs after the engine is started, it can be 
stopped by admitting live steam to the receiver and low-pressure 
cylinder. 

Main Bearings. — The main bearings, three in number, are of cast- 
iron shells split in halves, the lining and facing next to the cranks 
being of the best grade of babbitt. Wear may be taken up by filing 
or machining off the brass liners between the boxes. These liners 
also prevent the boxes from turning. Care should be taken to see 
that the liners are set close to the shaft so that the oil does not 
flow out of the ends of the boxes, causing a loss of pressure. 

The lower half of the box can be easily removed for repair or 
examination by slightly raising the shaft. 

Over the end bearings are hollow cylindrical cast-iron covers 2f 
inches in length with flanges for bolting to the column. Free 
access to the end bearings may be had by removing these covers. 



528 



Naval Electricians' Text Book 



Piston-Rod Packings.- — The piston-rod packing is shown in Fig. 
246 and is known as the " Class No. 1 " or " Double " type and is 
used on both the high-pressure and low-pressure rods. 

The packings consist of vibrating cups A and A receiving the 
packing rings, 1, 2 and 3. These rings are in halves and in 
assembling the packings care should be taken to see that the joints 






^ i/Var^Ce f=>/p><s one/ V<or/w<s 




Fig. 246. — Piston-Rod Packing. 



are broken. The vibrating cups rest upon rings B and B, which 
have a spherical bearing so that the packings will follow the rod in 
any position. The steam pressure forces the packing down in the 
cups and against the piston-rod, thereby preventing the leakage of 
steam. The coil springs C and C assist this pressure, at the same 
time holding the packing in place and preventing the rings from 



Motive Power eor Gexerators 529 

following the rod at the moment of reversal. When the packing 
has been taken out for examination or other purposes, the ground 
surfaces should be perfectly clean and free from grit before 
assembling. 

The box holding the packings is drilled and tapped for a -J-inch 
waste pipe and fitted with a globe valve which should at all times 
be open. 

General Electric Form H-2 Engine. 

This form of engine made by the General Electric Company 
replaced form H-l, and many of this design will be found on our 
later ships of war. It differs somewhat in its detail from form 
H-l, the principal difference being in the arrangement of the gover- 
nor which is removed from the fly-wheel casing and placed inside 
the engine casing. This form of engine is used with generators 
up to 100 kilowatts capacity. Its details will only be considered in 
the differences from form H-l, and all dimensions given are for 
the engine of the 100-kilowatt generating set. 

Steam Pressure. — The range of steam pressure for this engine is 
between 120 and 180 pounds, with a normal pressure of 150 pounds 
and 25-inch vacuum. The engine will carry an overload of 33-J 
per cent without trouble. It is advisable to maintain normal steam 
pressure, if possible. 

Cylinders. — The cylinders are 10 and 18 inches with a stroke of 
10 inches. The high-pressure and low-pressure cylinders are sepa- 
rate castings of hard, close-grained cast iron, accurately bored and 
externally covered with a thick layer of best quality asbestos, and 
are lagged with planished sheet iron. The high-pressure cylinder 
and steam chest are in one casting ; the low-pressure steam chest is 
bolted to the low-pressure cylinder. 

The receiver, forming a part of the cylinder castings, conveys 
the exhaust steam from the high-pressure cylinder to the low- 
pressure steam chest. 

Both cylinders have relief valves and are tapped for drain and 
indicator valves. The draining arrangement with 1-inch relief 
valve, swinging check valves and three-way indicator cock for high- 
pressure cylinder, is shown in Fig. 247. The 1^-inch relief valves 



530 



Naval Electricians' Text Book 



for the low-pressure cylinder are of the same general construction. 
The high-pressure steam chest cover and cylinder head, the low- 
pressure cylinder head, and the low-pressure steam chest cover and 
relief plate are shown in Fig. 248. 

The high-pressure and low-pressure cylinder heads are each 
fastened to their respective cylinders by twelve J-inch studs and 



Expansion i7o/rrt 




Pig. 247. — Draining Arrangement. 



nuts. The flanges of both heads and low-pressure steam chest 
cover are tapped for two f-inch eye-bolts for use in lifting these 
parts. 

The high-pressure and low-pressure cylinder heads are covered 
by polished cast-iron hoods. 

Valve-Stem Stuffing-Box. — Fig. 248 shows the valve-chest bonnet 
with stuffing-boxes. Ordinary soft packing of good quality may be 
used in these stuffing-boxes. 



Motive Power for Gexerators 



531 



High-Pressure Valve. — The high-pressure valve takes steam on 
the inside, the admission edges being at E, and the exhaust edges 
at F. 




Fig. 248. — Vertical Section of Engine. Form H-2. Gen. Elec. Co. 



The steam lap is § inch top and bottom ; the exhaust lap, top and 
bottom, is inch. The travel of this valve is controlled by the 
automatic governor, and varies between 3f and If inches. The 
cut-off varies between f and 0, depending upon the load. 



532 Naval Electricians' Text Book 

Low-Pressure Valve. — The admission edges of the low-pressure 
valve are at G, and the exhaust edges at H. 

The steam lap is 1^ inches and the travel of the valve 3f inches, 
giving a cut-off of about \ stroke. The exhaust lap, top and bot- 
tom, is inch. 

Eccentric Rod and Strap. — Fig. 249 shows the high-pressure 
eccentric rod and strap with forked brasses which are in three 
pieces. 

The low-pressure eccentric rod and strap are of the same general 
construction with the exception of the brasses which are in two 
instead of in three pieces. 



Pig. 249. — Eccentric Rod and Strap. 

These brasses are secured to the upper end of t*he eccentric rod 
by two f-inch studs, while the lower end of the rod is secured to 
the top half of the strap by two studs of the same size. 

The halves of the strap are kept a proper distance apart by 
liners which provide ample means of adjustment for wear and 
settings. 

The bearing caps A are each secured by studs and double nuts. 
The wear is taken up by filing the cap faces. 

The cast-iron guide for the high-pressure valve stem is bolted to 
the engine column, and is fitted with a composition metal bushing 
which is pressed into the guide. 

Piston and Piston Packing. — The high-pressure piston is shown 
in Fig. 250, and is a cast-iron disk containing two rectangular 
grooves, which receive the piston packing consisting of three cast- 
iron arcs, overlapping at the ends and made steam-tight by brass 
tongues, one of which is riveted to each arc. The packing is held 



Motive Power eor Generators 



533 



tightly against the cylinder by flat springs f -inch wide and -^ -inch 
thick, which are fastened to the arcs by small machine screws. The 
piston fits on a taper and against a shoulder on the piston-rod and 
is secured by a nut on its upper side. The outer face of this nut 
contains radial grooves, one of which engages a split pin which 
prevents the nut from unscrewing. 





Fig. 250. — Piston, Piston-Rod and Piston Packing. 



The low-pressure piston is also of cast iron, the general construc- 
tion being the same as that for the high pressure, excepting that the 
packing is in four instead of in three sections, and that the piston 
is cored instead of being solid. 

Piston-Rod. — The piston-rod (Fig. 250) is of nickel steel, and 
the diameter of both the high and 
the low-pressure rods is 3J inches. 
Each rod is threaded at the lower 
end which screws into the cross- 
head and is locked by a spanner 
jam nut. 

Cross-Head. — The construction 
of the cross-head is plainly shown 
in Fig. 251. The body A is a 
mild steel forging. The cross- 



head shoe B is of composition 
metal, babbitted, and has a very 
liberal wearing surface so that the 
wear at this point will be very 



D^ 




Cross-Head. 



534: 



Naval Electricians' Text Book 



slight. The cross-head shoe is fastened to the cross-head by two 
1-inch holts and is held against the guide bar by the clamp C which 
is connected to the shoe by six through bolts, the proper distance 
between the shoe and clamps being maintained by adjustable 
liners D. 

The cross-head is slotted to receive the wrist-pin bearing E which 
is made of gun metal, and is held in place by cap F and two bolts 
secured by lock-nuts G. The upper part of each nut is turned 
circular, and fits in a recess in the cap. Set-screws H prevent the 
nuts from turning, and set-screws J prevent the turning of the bolts. 

Wear may be taken up by filing the edges of the brasses, and on 
account of the system of oiling which is used in this engine, it is 
important that these edges should always be together. The bearing 



Governor We/g^it Pm 
&/ Def/ector . ♦ f 




Fig. 252. — Crank-Shaft and Coupling. 



should be so adjusted that when the brasses are hard together the 
wrist pin will move freely but without any play. Oil reaches the 
bearing from the oil pipe, passing up the side of the connecting 
rod; from this bearing it is further forced to the guide. 

Crank-Shaft and Coupling. — The crank-shaft and coupling (Fig. 
252) for transmitting the power to the generator, are made in one 
solid piece of forged steel with the crank-pins machined out. 

Cast-iron counterbalance weights are fastened to each crank oppo- 
site the crank-pin, to balance the moving parts. Each weight is 
held by two bolts, one a cap bolt with the head sunk in the weight, 
the other a through bolt passing through the crank and secured 
by a nut. 

One of these v/eights acts as a support for the adjusting screw 
of the governor spring. 

One end of the shaft receives the balance pulley and the opposite 



Motive Power for Generators 



535 



end holds part of the coupling. The two parts of the coupling are 
held together by four lj-inch bolts, and are forced apart by two 
f-inch set-screws when it is desired to disconnect the armature. 

The radial key, 1-inch square, for transmitting the power, is 
secured to the face of the coupling by two -^-inch flat-headed 
screws. 

The shaft has a diameter of 5 inches at the bearings and -ij 
inches at the pulley end. 

Throttle-Valve. — Fig. 253 illustrates 
the throttle-valve furnished with each 
engine. It is of the Lunkenheimer, re- 
grinding type, and is 3-| inches in 
diameter. The valve is fitted with a 
by-pass integral with the body. The 
valve stem is carried outside of the 
valve through the yoke, and a bolt and 
gland stuffing-box is used. 

To regrind the valve seat when worn 
and leaky, proceed as follows: If the 
main valve, unbolt the bonnet, take the 
nut from the end of the stem, and re- 
move the hand-wheel, after which re- 
move the entire trimming from the 
valve body. The stem can then be 

unscrewed and drawn from the yoke. Prepare some abrasive 
material, such as a little powdered glass, sand or carborundum, mix 
it with oil, and apply this to the disk. Make the disk rigid with the 
stem by inserting a nail or piece of wire through the drilled hole 
below the lock-nut. The valve can then be reground by fastening 
the hand wheel to the stem, the extension of the disk being guided 
by a bridge in the body of the valve, which will enable the new 
seat bearing to be reground in perfect alignment. When the valve 
is reground, care should be taken to wipe off all the abrasive ma- 
terial from the seating surface, and to remove the wire pin from 
the disk. When properly reground, the valve will again be steam- 
tight. 

The by-pass is not provided with a grinding-in guide, but, on 




Fig. 253.— Throttle-Valve. 



536 



Naval Electricians' Text Book 



account of its small size (^ inch), and also on account of the 
spherical seat, the guide is hardly necessary. It can be reground 
by using the same abrasive. 

All other valves used on this engine are of the same make, and of 
the union-bonnet construction, therefore it is necessary to re- 
move the stem from the valve trimming, as the hub of the trim- 
ming should guide the body and keep the stem in line with the seat, 
otherwise the regrinding is accomplished as above noted. 

Governor. — The governor is illustrated in Fig. 254, and consists 

of a single fly-weight A in halves 
which are securely bolted together 
and pivoted at B to the main 
bearing pin which is driven into 
the crank and secured by a set- 
screw as shown in the illustra- 
tion of the crank-shaft. The fly- 
weight is supplied with a loose 
brass bushing which provides a 
double bearing surface. The pin 
and bushing communicate with 
the inside of the engine and are, 
therefore, always under an oil 
pressure which reduces to a minimum the danger of sticking or 
binding. 

The operation of the governor is as follows : 
The eccentric rod and strap (Fig. 249) which transmit motion 
from the governor to the high-pressure valve are connected to the 
eccentric C forming a part of the weight casting. It is therefore 
evident that the length of the valve stroke depends upon the dis- 
tance of the center of the eccentric C from the center of D. 

The amount of steam admitted to the cylinder varies directly as 
the distance between the centers of C and D; that is, the less the 
distance the less the amount of steam admitted, and vice versa. 

Suppose the speed of the engine to increase ; the weight A is 
immediately drawn out by centrifugal force, thus decreasing the 
distance of the center of C from the center of D and reducing the 
amount of steam admitted to the cylinder. Should the speed of 




Fig. 254. — Governor. 



Motive Power for Gexerators 



537 



the engine approach a dangerous point, the distance of D from 
the center of C will be diminished until the minimum distance is 
reached, when the steam is entirely cut off from the cylinder. 

The motion of the fly-weight is opposed by the spring E which 
is attached to a bracket cast with the crank-shaft counterbalance. 
By increasing or decreasing the tension of the spring, the speed may 



Oil Pumpfccentr/c 



ToLP/4>/eO 




Ya/ises 

Fig. 255. — Lubricating Mechanism. 



be raised or lowered. The same effect will be produced by moving 
the spring in the slot of the weight — moving it away from the 
fulcrum increases the speed and towards the center produces the 
opposite effect. 

Unstable regulation is due, principally, to too close an adjustment 
of speed and may be avoided by moving the spring attachment away 
from the fulcrum. 



538 Naval Electricians' Text Book 

The governor should occasionally be taken apart and cleaned, 
and care should be taken to see that the oil hole leading to the 
governor weight pin and bushing is kept free from all foreign 
substance. This is best accomplished by never allowing any waste 
or dirt to enter the inside of the column and thus find its way to 
the different bearings. 

Lubrication. — The lubricant is carried under pressure to the 
various parts of the engine by the mechanism shown in Fig. 255 
and will be understood from the description given for the form 
H-l engine. 

Indicator Motion. — When it is desired to indicate the engine, a 
small cover must be removed from the front of the column, exposing 
a slot over which a bracket containing a bearing pin for the levers 
is attached. Each cylinder has its own indicator motion consisting 
of a stud screwed into the wrist pin of the connecting rod for 
driving the motion, which connects through a link to a lever pivoted 
to the bracket covering the slot in the column. The motion for 
the indicator is taken from a cord pin on this lever. 

Starting the Engine. — Before steam is admitted to the cylinders 
care must be taken to see that the valves move freely. This may 
be done by turning the balance pulley by hand. As the expansion 
of the valves is much more rapid than that of the cylinders, the 
cylinders should be allowed to attain their proper temperature be- 
fore full pressure is applied. A by-pass valve J inch in diameter, 
integral with the body of the throttle-valve (see Fig. 253), is used 
for the purpose of heating the engine before starting. The drain 
from the steam chest together with all the cylinder-drain valves 
should be kept open, to allow all condensed water to escape. 

If water hammering occurs after the engine is started, the 
cylinder-drain valves should be quickly opened. 

Engines for Torpedo Boats. 

These are made for generators of 2J and 5-kilowatt capacity 
installed on torpedo-boat destroyers and torpedo boats. They are 
of the single cylinder, vertical, double-acting type designed for 
either 700 or 800 revolutions per minute at full load with 100 
pounds steam pressure. 



Motive Power eor Generator: 



539 



A generating set of 5 kilowatts using this engine is shown in 
Fisr. 256. The engine is enclosed in a sheet-iron case which has 
been removed to show the moving parts. 

There are no points of unusual detail in this engine, and the 



1 


1 ; 


1 

•> 






1 




■ 


L_ 


I 


mPi 





Fig. 256. — General Electric Company's M. P. 6-5-700, Generating Set. 



only description given is that of the governor which is shown in 



Fig. 9 



507. 



The governor is a modification of the Eites design and is shown 
in Fig. 257'. It is placed inside of the fly-wheel and on its outer 
side. The fly-wheel, A, is keyed to the shaft and carries the gover- 
nor parts, consisting of : a weight B, pivoted at C; an eccentric D, 



540 



Naval Electricians' Text Book 




Fig. 257. — Governor. 



with counter-weight E ; a coiled spring F, taking by a knife-edge 
on teetli at the upper side of the weight; and a link G, connecting 
the weight to the end of the bell crank of the counter-weight. 

The operation of the gover- 
nor is as follows: The eccen- 
tric strap, which transmits mo- 
tion from the governor to the 
valve, is connected to the eccen- 
tric D; the travel of the valve, 
therefore, depends upon the 
distance of II from the crank 
K. If the speed increases, the 
weight B is immediately 
thrown by centrifugal force to- 
ward the perimeter of A, de- 
creasing the distance between 
H and K and shutting off 
steam from the cylinder ; if the 
speed becomes too great the minimum distance between II and K 
is reached and practically all steam is shut off. Control of sjoeed 
is effected by the tension of the 
spring, increasing the tension 
increases the speed and vice 
versa. The same effect will re- 
spectively be produced by mov- 
ing the knife-edge suspension 
away from or towards the ful- 
crum 0. 

The governor for the engine 
used with the 2-J-kilowatt set is 
shown in Fig. 258. 

The governor is a modifica- 
tion of the Rites design and is 
shown in Fig. 258. It is 

placed inside of the fly-wheel or pulley and on its upper side. The 
pulley A is keyed to the shaft and carries the governor parts, con- 
sisting of two weights B and B r connected to the opposite ends of 




Fig. 258. — Governor. 



Motive Power for Generators 541 

the lever C, on which is the pin D operating the valve. The centri- 
fugal force of the weights is opposed by the leaf springs which are 
connected to the fly-wheel by the studs F and F' with double nuts, 
and which fulcrum on G and G'. The springs are held in place by 
flanges on the ends of the fulcrums. 

The operation of the governor is as follows : The governor con- 
necting rod which transmits the motion from the governor to the 
valve, is connected to D; the travel of the valve, therefore, depends 
upon the distance of D from the' center of A. If the speed in- 
creases the weights B and B' are immediately thrown by centri- 
fugal force toward the perimeter of A, decreasing the distance of 
D from the center of A and shutting off steam from the cylinder; 
when D and the center of A nearly coincide practically all steam is 
shut off. 

Other Types of General Electric Engines. 

Besides the types described, the General Electric Company fur- 
nishes engines that have been used on torpedo boats, auxiliaries, 
colliers, etc., called form A, B, C, D, etc. These are of a com- 
mercial type and are of the vertical, inverted, reciprocating, simple, 
condensing or non-condensing, double-acting type. 

The Forbes Engine. 

A section of a Forbes engine is shown in Fig. 259. It has several 
features differing from those previously described, among which 
are the kind of piston-rod packing, the form of governor and the 
control of the value by the governor. 

The governor controls the low-pressure valve in the Forbes 
engine and not the high-pressure as in the types of the General 
Electric Company. 

Governor. — There are two types of governor used with the 
Forbes engine, both constructed on the Bites design. 

The weight embraces the greater part of a circle and is attached 
to a cross-arm pivoted as shown. The spring controls the centri- 
fugal motion of the weight in the usual way. The fulcrum of the 
spring is adjustable in a slot. The action and adjustments are the 
same as for other governors built on the Bites design. 



542 



Naval Electricians' Text Book 




Motive Power for Generators 



543 



The type used with smaller engine designs is shown in Fig. 260. 
It is a modification of the Corliss type of the Rites design. The 
governor standing part is an iron casting keyed to the shaft. At 
one side of the shaft is an extension which is bushed to form the 
bearing for a stud extending from the governor weight, and in 
the opposite direction is an extension which forms the outer point 
of attachment of the governor spring. The governor weight is a 
cam-shaped iron casting. The parts of the wheel face between the 
arms (or spokes) are arched out to reduce shrinkage strains, and 
to reduce, by a multiplied fluttering, the optical effect of the gover- 
nor's eccentric rotation. To one of the six arms is attached a stud 





Fig. 260.— Governor for 24 K. W. and Below. 



which forms the inner point of attachment of the governor spring. 
The eccentric pin is of machine steel and extends outwardly from 
the hub of the governor weight. The governor weight-retaining 
plate is a composition casting which is secured by two fillister-head 
machine screws to two extensions of one of the governor arms and 
engages with a projection at the governor standing part to keep the 
governor in position longitudinally on the stud. When any 
" sticking " occurs with this type of governor, it will usually be 
found in a too tight setting up of the cap nut that secures the 
weight. 

The piston-rod packings are metallic, of the Katzenstein type; 
those on the high-pressure and low-pressure piston-rods are similar 
and of the " sectional self-acting " form, and are shown in Fig. 



544 



Naval Electricians' Text Book 



2G1. In the lower cylinder heads is a large bushing, A, which 
forms a guide for the piston-rod and a surface against which the 
packing rings are placed. Each ring has a serial number ; the 
rings are placed in position in the sequence of their numbers. 
Eings No. 1, B, No. 3, D, and No. 5, F, are of bronze and cut in 
segments ; these form conical surfaces forcing into place the packing 
rings No. 2, C, and No. 4, E, made of special anti-friction metal. 
Eings No. 2, C, and No. 4, E, are also cut in segments, in the 
placing, the joints are staggered with reference to the segments of 




HIGH *nb LOW PRESSURE 
PISTON RODS 

Fig. 261. — Katzenstein Metallic Packing. 



rings No. 1, B, No. 3, J), and No. 5, F. It will be noted that rings 
No. 1, B, and No. 3, D, and No. 5, F, do not come in contact with 
the rod, but leave spaces between their edges in which the water of 
condensation may collect. In the space, G, below the rings, fibrous 
packing is placed, increasing the elasticity of the contact of the 
rings and facilitating lubrication. The gland, H, is of bronze and 
guides the piston-rods at their lower ends. A groove turned in at 
J is drilled with a drain hole, K. Below this is an auxiliary stuf- 
fing space, L, in which a turn of fibrous packing is placed and 
retained by the bronze gland M. 



Motive Power for Generators 



545 



The B. F. Sturtevant Engine. 

A cross-sectional view of one of the larger engines of this make 
is shown in Fig. 262. 

It resembles in its general features the engine built under the 
same specifications by the General Electric Company. The gover- 




Fig. 262. — B. F. Sturtevant Company's Engine, 100 K. W. 



nor is of the Eites " dumb-bell " type and is mounted on the out- 
side and inside the fly-wheel. The governor controls the high- 
pressure valve and the high-pressure eccentric is mounted on a 
pin extending through the fly and governor wheel. As the weight 
flies out under the action of the centrifugal force, the eccentric is 
moved and the travel of the valve is shortened. 



5-A6 Naval Electricians' Text Book 

Steam Turbines. 

The latest form of generator driving adopted is the steam tnrbine 
and generating sets of 300-kilowatt capacity with this form of 
motive power are now being built under the following specifications : 

Turbine. 

1. The turbine will be of the horizontal multi-stage type. It will be 
designed to run condensing with maximum practical efficiency at all 
loads. It will be of sufficient power to drive the generator for an 
extended time at the rated speed when said generator is carrying 
ly 3 load. 

2. The normal steam pressure under which the turbine will operate, 
and at this steam pressure the maximum steam consumption in pounds 
per K.-W. hour for various degrees of vacuum, is: 

K ' -W - pressure. 25" Vac. 26" Vac. 27" Vac. 28" Vac. 

300 265 gauge 26 25 23£ 

These rates should be interpreted as dry saturated steam, steam pres- 
sure being measured at throttle and vacuum in exhaust casing. Super- 
heated steam shall not be used in the test. 

3. The turbine to run smoothly and furnish the required power for 
full load at any steam pressure within 20 per cent (above or below) 
of those given in the table, and exhausting to condenser at 25 inches 
of vacuum; to furnish power for full load at any steam pressure 
between normal and 20 per cent above normal, when exhausting into 
the atmosphere. It will bear without injury the sudden throwing on 
or off of one and one-third times the rated load of the generator by 
making and breaking the generator's external circuit. 

4. The steam inlets shall be so placed as to admit of piping from 
either side with equal facility. Blank flanges shall be furnished com- 
plete, when required to cover alternative outlets. Turbine to have 
exhaust outlet on right or left side as specified. All piping shall be 
firmly supported at points close to the turbine, so that the weight of 
same shall not affect the alignment of the parts involved. 

5. Steam inlet valve shall be a combination throttle and emergency 
valve equipped with strainer intervening between valve and turbine 
steam line. It will be connected to the emergency governor in such 
a way that it will automatically close if the speed of the turbine rises 
more than 10 per cent above normal. Flange drilling to conform with 
specifications of the Bureau of Steam Engineering. 

6. The governor will be of the centrifugal type operating a series of 
valves. 



Motive Power for Generators 547 

7. Lagging shall be fitted as extensively as practicable to turbine. It 
shall be done after a preliminary run of the turbine in order that any 
defects in casting or joints may be readily found. The arrangement 
for securing the lagging in place shall admit of its ready removal, 
repair, and replacement. 

8. The speed variation will not exceed 2 per cent when load is varied 
betwen full load and no load gradually or in one step, turbine running 
with steam pressure normal or 20 per cent above normal, and exhaust- 
ing into 28-inch vacuum. A variation of not more than 4 per cent will 
be allowed when full load is suddenly thrown on or off the generator 
with steam pressure constant between normal or 20 per cent above 
normal and exhausting into the atmosphere. No adjustment of the 
governor or throttle-valve during the test shall be necessary to insure 
proper performance under the above conditions. 

9. The turbines will operate without the use of lubricants in the 
steam spaces. Forced lubrication will be used on all bearings. The 
bed-plates will contain an oil reservoir from which oil will be drawn 
by a pump operating directly from the main shaft, and forced through 
the system. To be provided with a strainer which may be removed 
without interrupting the oil supply. The oil will be cooled by water 
which will pass through a coil around which the oil will circulate. 

10. Mandrels, with collars, complete, will be furnished for renewing 
the white metal of all bearings so fitted. 

11. The material and design of the turbine will be such as to safely 
withstand all strains induced by operation at the maximum steam pres- 
sure specified. 

12. The maximum allowable normal speed, weight and over all dimen- 
sions of the complete generating set, of which the turbine forms the 
motive power are: 

f3*» R.P.M. ^ OjSff ££32" Width. Height. 

*- w * mios. lengin. connections. 

300 1500 28,000 155" 100" 76" 90" 

Elementary Theory of the Curtis Steam Turbine. 

The following general theory of the steam turbine is taken from 
a paper on " The Curtis Vertical Steam Turbine " by Charles B. 
Burleigh of Boston, Mass., and reproduced by permission of the 
author : 

" The Curtis turbine bears a strong resemblance to a water-wheel 
and most of the principles involved are applicable to both. The 
widest difference, however, between steam and water is in the 
speed at which they move under pressure. 



548 Naval Electricians' Text Book 

" The velocity of a jet of water at 150 pounds pressure per square 
inch, which is equal to a head of 346 feet, is approximately 149 
feet per second, while steam expanded from 150 pounds pressure 
per square inch to the pressure of the atmosphere attains a speed 
of 2950 feet per second and if expanded into a 28-inch vacuum can 
attain a velocity of 4010 feet per second. It will, therefore, be 
noted that the speed of steam is 19 times that of water at 150 
pounds pressure. 

" There are certain fixed laws governing wheels actuated by fluids 
which are productive of the best results : the buckets should, to pro- 
duce the best results, move at one-half the speed of the fluid which 
actuates them and any departure from this condition results in 
lessened efficiency. There should be no shock between the buckets 
and the fluid, no sharp angular deflection to suddenly change the 
direction of motion of the fluid; there should be as little friction 
as possible between the buckets and fluid. 

" There are many other characteristics of importance which will 
become apparent as we continue. 

" Velocity of Steam. — As in actuating the turbine we are inter- 
ested only in the velocity and volume of the steam and have no 
interest in the expansion other than for the production of the 
resulting speed and from the fact that until the comparatively 
recent development of the turbine, steam engineers have paid little 
or no attention to this characteristic, it may be well to briefly 
discuss it. 

" Let us consider a given volume of steam at a given pressure, 
confined in a vessel surrounded by a similar vessel in which the 
pressure is equal to that of the steam in the inner vessel. For the 
sake of simplifying the illustration, disregard temperature. If we 
effect an opening in the inner vessel no steam will escape into the 
outer one, for the reason that the pressures are balanced. Now, if 
by any means we lower the pressure in the outer vessel equilibrium 
is destroyed and the steam immediately expands to this lower 
pressure, just as it does in the engine cylinder behind the moving 
piston. 

" The steam cannot expand without displacement of the medium 
before it and the energy of expansion is utilized in producing motion 
in the steam mass. 



Motive Power for Generators 549 

" The steam in its confined state was possessed of potential energy 
and on expanding a part of this potential energy was converted 
into kinetic energy or velocity. 

" It is a fact not generally appreciated that this kinetic energy 
generated by the expansion of a given weight of steam depends 
upon the number of times the steam is expanded and not npon the 
particular pressures between which it is expanded; or, in other 
words, 1 pound of steam expanded from 4 to 2 inches absolute 
pressure (26 to a 28-inch vacuum) at atmospheric pressure of 30 
inches of mercury or from 2 pounds to 1 pound absolute, is capable 
of as much work as expanding the same pound of steam from 150 
pounds to 75 pounds pressure. This is very clearly illustrated in 
diagrammatical form in an article written and published in 
' Power/ October 9, 1905, by its editor, Mr. Fred. E. Low. 

" "Without expansion, steam is incapable of motion, but other 
things being equal its motion is in accordance with its expansion, 
that is, its acceleration is increased as the difference in pressures 
between which it is expanded is increased. 

" In the Curtis turbine the steam is expanded in a series of ex- 
panding nozzles so designed that they will expand it between such 
pressures as will give to the steam the desired velocity to which we 
shall refer more in detail later. 

" For the present, let us consider two facts : 

'• First. That steam expanded from 150 pounds pressure to that 
of the atmosphere will acquire a velocity of 2950 feet per second. 

" Second. That in order to efficiently utilize this velocity it is 
necessary that the actuated medium (the buckets) move at a speed 
one-half that of the steam actuating them. Therefore, in this 
case, the bucket speed to meet these conditions must be 1475* feet 
per second. Let us consider these buckets milled on the periphery 
of a wheel 1 foot in diameter and it will at once become apparent 
that this wheel must rotate at a speed equal to a circumferential 
speed of 1475 feet per second, which would result in a shaft speed of 

., ... . — = 28,170.3 revolutions per minute. 
<3.141b l 

** It is obvious from the foregoing that a means must be devised 

whereby we shall be enabled to overcome this excessive speed. In 



550 Naval Electricians' Text Book 

order to arrive at a solution of this problem in proper sequence let 
us more fully investigate the interaction of the buckets and steam 
and their effect on each other. 

" The shape of the Curtis bucket may best be compared to a ver- 
tical new moon, so arranged that the steam is brought in contact 
with it at the top, at an angle corresponding closely to the arc of the 
buckets. When the flowing steam is brought in contact with the 
buckets, which, due to their shape, tend to change its direction of 
flow, it tends to move these buckets. 

" ISTeglecting losses the velocity of the steam on leaving the bucket 
equals the velocity at which it enters it. 

" If the bucket is in motion the nozzle delivering the steam being 
stationary, the velocity of the steam leaving the bucket will, instead 
of equalling the entrance velocity, equal the . difference between the 
bucket velocity and the entrance velocity; that is, the steam in 
travelling faster than the bucket, and following around the curve of 
the bucket, leaves it with a velocity relative to the bucket, the same 
as that at which it entered. 

" Mr. J. G. Callan, of Lynn, gave an explanation of this in a 
recent lecture which describes this action most clearly : c Steam 
enters the bucket at velocity V 1 , follows the arc of the bucket and 
neglecting losses, the velocity which is left is V 2 . 

" i The weight of the steam has remained unchanged and since 
the energy of a moving body is one-half the mass, times its velocity 
squared, the energy possessed by the steam as it goes into the bucket 

MY 2 • • MV 2 

is l . Its energy as it comes out is 2 and the energy given 
2 Z 



up for the bucket is ( — ~-± j — I 2 j . 



" l This has been given up to the buckets because the steam was 
pushing while the buckets were moving. 

" ' If the buckets had been stationary it would have simply 
changed the direction of the steam without material loss of energy, 
as it would have entered at a velocity of V ± and left it at practically 
the same velocity. 

" ' Do not understand that the steam would not tend to actuate 
the stationary bucket, for it would, for the pressure on the bucket 



Motive Power for Generators 551 

is greater when the bucket is stationary and is reduced as the bucket 
moves away from the steam, as the steam pushes the bucket under 
these conditions with the lessened velocity. 

" ' If the bucket is held stationary no work is being done. Work 

is represented by the formula — - — , also by FS or force multiplied 

by space. 

" ' If force acted upon the bucket without moving it, no work 
would be done. The steam delivered by the nozzle is moving so 
fast that it is not at all inconvenienced in keeping up its push on 
buckets moving at a high speed, and as we increase the velocity of 
the bucket the steam is able to follow it and tends to push it for- 
ward up to a velocity equal to that of itself; if the speed of the 
bucket reaches that of the steam the steam would simply follow it 
without pushing at all. Bear in mind that it is the proportion of 
the volume of the steam to the resistance to the movement of the 
bucket which determines the speed of the bucket. 

" ' From the foregoing it is easy to determine the best speed 
conditions. When the bucket is stationary the push is greatest 
and its velocity is zero and when the speed of both the steam and 
the bucket are equal the velocity is greatest and the push is zero; 
at both these extremes the work done is zero. 

" ' There is a point between these two extremes where the effect 
will be maximum. That point will be where the energy remaining 
in the steam after it has passed through the bucket will be the least. 

" i Xow let us assume that V 1 is just twice the velocity of the 
bucket, then subtracting this bucket velocity from the steam 
velocity, leaving the remainder as the speed of overtaking, and then 
subtract the same bucket velocity from it again and we shall have 
subtracted the half of V x twice and V 2 will become zero; in other 
words, with the bucket moving at one-half the speed of the steam 
which actuates it the velocity remaining in the steam is zero and it 
is clear that we have obtained maximum efficiency. 

" ( But as previously stated, we are in trouble due to the excessive 
shaft speed resulting from the bucket speed necessary to maintain 
these conditions. There are two methods by which we can reduce 
our shaft speed without resorting to gears: First. We can cause 



552 Naval Electricians' Text Book 

the steam to acquire its full velocity, cause it to actuate the buckets 
of the first moving wheel and give up a certain amount of velocity, 
then pass it through stationary re-directing blades and cause it to 
actuate the buckets of a second wheel and give up to it more of its 
velocity and pass it on by the same method to a third and even a 
fourth wheel. 

" ' Another method is to utilize during the first step part of the 
energy of the steam for acceleration, that is to say, expand it from 
boiler pressure to say one-half or one-quarter of the exhaust 
pressure. 

ec ' It is obvious that by this method we have transformed only a 
part of the potential energy of the steam into kinetic energy and 
by so doing have caused the steam to move at a proportionately 
lower speed. 

" 6 We may now expand it further by as many steps as are found 
to be desirable. Either of the foregoing methods will result in 
enabling us to reduce our shaft speed. Considering the second- 
method, suppose we take a four-stage turbine compared with a 
single stage, with one wheel per stage in each. It would appear at 
first glance that by the use of four stages we should reduce our 
shaft speed in the ratio of four to one, but this would not be the 
case. The steam admitted to each of the four stages will have one- 
quarter of the total energy, equal to one-half of the steam velocity, 
which would result, if all the energy were used to produce velocity 
in one stage. Now the economical wheel must move at a peripheral 
speed which is proportional to the velocity and not the energy of 
the steam which actuates it and as the steam velocity has only been 
halved by using four stages, we have only reduced our shaft speed 
by a like amount, assuming a single wheel per stage. 

" e Therefore, by this method shaft speed is reduced as the square 
root of the number of stages used. 

" ' Let us now investigate the first method of reducing shaft 
speed. If, as before stated, we expand the steam completely in 
the nozzle and obtain full velocity, and actuate but one wheel with 
it, the wheel must move at a peripheral speed equal to about one-half 
of the velocity of the steam, in order to produce the best results. 
Xow if we can devise a means by which we can redirect the steam 



Motive Power for Generators 553 

as it emerges from this wheel and bring it in contact with a second 
wheel, this second wheel moving at the same speed and in the same 
direction as the first, will extract practically the same amount of 
velocity from the steam, so each of the two wheels need have but 
half the peripheral velocity of the single wheel. Therefore, by the 
use of two wheels, we reduce the shaft speed to one-half. Now let 
us combine the two methods and note the result. 

" i Let us expand our steam from boiler pressure in a set of 
admission nozzles to, say, within three-quarters of exhaust pressure 
and with it actuate the buckets of a first-moving wheel, where it 
will give up a certain amount of velocity, then pass it through a 
set of stationary redirecting blades, and cause it to actuate the 
buckets of a second wheel which shall abstract the balance of its 
velocity. After leaving this second wheel the kinetic energy of 
the steam is exhausted but it still possesses potential energy, from 
the fact that it is capable of further expansion. 

" ' We have now passed what is termed the first stage. Let us 
now deliver the steam to a second set of expanding nozzles which 
will permit it to expand to within one-half of the exhaust pressure, 
thus giving velocity to the steam equal to the first expansion, and 
deliver it to two similar wheels and set of redirecting vanes where 
the same process is repeated, resulting in the velocity being reduced 
to zero and the steam brought to rest. 

" ' We have now passed what is termed the second stage, but the 
steam still possesses potential energy, being capable of further 
expansion. 

" ( We now deliver it to a third set of nozzles which expand it to 
within one-quarter of exhaust pressure, thus producing a steam 
velocity equal to each of the previous expansions and deliver it to 
two more wheels and set of redirecting vanes, with the same result, 
passing now what is termed the third stage. 

" ' Here we deliver the steam to a fourth set of nozzles which 
expand it to exhaust pressure, again imparting to it a velocity equal 
to what it possessed on entering each of the three previous stages, 
which velocity is abstracted in a similar manner by two more 
wheels and set of redirecting vanes. We have now passed what is 
termed the fourth stage, and have abstracted from the steam all of 
its energy. Now let us see what we have accomplished. 



554 



Naval Electricians' Text Book 



" ( Our bucket speed is, in each case, half our steam speed and 
we have halved this twice, first by doubling our number of wheels 
per stage and second by increasing the number of stages. This has 
resulted in a very comfortable bucket speed and, due to the diame- 
ter of the wheels, we are enabled to use with this design, a very 
reasonable shaft speed/ " 

Oil Engines. 

Oil engines are used in shore wireless stations as power for 
generator driving at such places where a steam plant is not neces- 
sary for other purposes. These engines are always ready for use, 




' t 



Fig. 263. — Four-Cycle Compression. 



are simple in construction and do not require expert care or 
attention. 

A form of engine using oil as fuel extensively used in such 
isolated places as wireless stations is of the Hornsby-Akroyd make, 
built on the Otto cycle, or four-cycle compression type. 

The operation of a four-cycle compression is illustrated in Fig. 
263. 

First Period. Admission of the Charge.— The piston is driven 
down and a vacuum is created behind it through which the charge 
is drawn as shown by the open admission valve. This charge may 
be air and gas or vapor, and is drawn in throughout the first stroke 
of the piston. 

Second Period. Compression. — On the start of the return stroke 



Motive Power for Generators 555 

the admission and exhaust valves are closed, so that the mixture 
drawn in during the first stroke is compressed in the clearance 
space between the end of the cylinder and the piston. 

Third Period. Ignition. — At the end of the second stroke, the 
compressed mixture is ignited and the expulsion due to its explo- 
sion drives the piston to the end of the third stroke. 

Fourth Period. Exhaust. — On the return of the piston on the 
second stroke, the products of the combustion are discharged 
through the exhaust valve. 
D 




Fig. 2G4.— Indicator Card of Otto Cycle. 



This constitutes the four-period operation, each complete opera- 
tion consisting of four distinct periods, during which time the 
engine makes four strokes and two revolutions, and during which 
there is one explosion. 

Indicator Card. — The distinct operations taking place during 
one explosion can be seen from a typical indicator card shown in 
Fig. 264. 

AH represents the atmospheric pressure. From A to B the 
charge is drawn in on the first stroke of the piston and the pressure 
falls slightly below the atmospheric pressure. During this time the 
admission valve is open and the exhaust closed. The line BC repre- 
sents the pressure line due to the compression on the second stroke, 
and AC is the pressure of the charge due to the compression. 
During this operation both admission and exhaust valves are closed. 
The line CD represents the increase of pressure due to the igni- 



556 Naval Electricians' Text Booe: 

tion of the mixture, DE is the fall of pressure due to onward 
motion of the piston in the third stroke, and at E, the exhaust valve 
opens and the pressure falls according to the line EF. On the 
fourth stroke, the exhaust valve is open and the products of com- 
bustion are discharged, the pressure falling according to the line 
FA, returning to the starting point. This operation is then re- 
peated over and over again. 

The Hornsby-Akroyd Engine. — This make of engine is of the 
four-cycle type and uses kerosene or any heavy mineral oil as fuel. 
A sectional view of this engine is shown in Fig. 265 showing the 
cylinder and combustion chamber. A represents the compression 
space into which the piston does not enter. Secured to the end of 
this compression chamber is the receptacle B which acts as a vapor- 
izer and exploder. In this engine the charge is exploded by spon- 
taneous ignition, the walls of the vaporizer being kept at a red heat 
by the combustion of the oil. To start the engine the vaporizer is 
heated by a lamp until brought to a red heat, when the lamp is 
extinguished and the engine started by hand. After once started 
the heat of the vaporizer is maintained by the heat due to the 
explosion. 

On the first or suction stroke a small quantity of oil is injected 
through a nipple directly into vaporizer, where it is vaporized by 
the intense heat. At the same time oil is injected the air valve is 
opened. At the end of the suction stroke the cylinder is filled with 
air and the vaporizer with oil vapor. During the compression 
stroke the air is compressed into the vaporizer where it mixes with 
the oil vapor and forms an explosive mixture, where it is ignited 
by the hot walls of the vaporizer. During the third stroke, the 
cylinder is filled with the products of the explosive mixture and on 
the fourth stroke all these products are forced out through the 
exhaust valve and another injection of oil takes place. 

The half of the vaporizer nearest the cylinder is covered with a 
water jacket, the other half unjacketed to maintain the red heat 
required. 

There is no vaporization until the oil is actually in the com- 
bustion chamber and the density of the oil is of no importance 
and light or heavy mineral oils may be used. The oil supply is 



Motive Power eor Gexerators 



557 



regulated by a governor and if the speed exceeds the normal the 
mechanism opens a b}*-pass valve which reduces the charge entering 
the vaporizer and the mean pressure developed in the cylinder. 




L^^^ 



CHAPTER XXIII. 
SWITCHBOARDS AND DISTRIBUTION PANELS. 

The general idea of a switchboard is to distribute the generator 
current throughout the ship according to some previously-designed 
plan; the method of distribution depending upon the total power 
and the purposes for which it is to be utilized ; whether for lighting 
power or search-light purposes, or any or all of them. In the early 
days of ship lighting the demand for current was small and the 
distribution very simple, usually one generator being sufficient to 
furnish all the desired current, and the switchboards were very 
simple, but very massive affairs. As the demands for current in- 
creased and the search-lights were furnished from the same source 
of power as the incandescent lights, one generator was not sufficient, 
so means had to be adopted of providing a switchboard that would 
distribute current for both kinds of lighting in parallel and to fur- 
nish a means of connecting the generators in parallel. 

A standard switchboard was adopted which was installed on many 
ships, and even now is to be met with frequently. The details of 
the switchboard proper are shown in Fig. 266. 

Fig. 266 represents a switchboard for two generators. On the 
board which is made of slate are mounted six vertical bus bars, the 
outside ones being connected together by a cable on the back of 
the board, shown by the dotted lines. This makes a common 
-f- bar for both generators, a generator lead from each positive 
terminal leading to the terminals of the bus bars. The four inside 
bus bars are negative bars, and they are connected to each other 
as shown by the dotted lines, representing connecting cables. This 
has the effect of making simply two negative bars, adjoining bars 
being connected to different machines. There are two terminals 
at the bottom of the board to which are connected the equalizer 
leads from the brushes of each machine. The negative bars of the 



Switchboards axd Distribution Paxels 



559 



two machines may be connected by a double switch as shown at the 
bottom of the board, one leg of the switch connecting the negative 
bars, the other the equalizer terminals. 

Circuit feeders leading from the switchboard to their feeding 






«'« 



»e i 



^ 



ill 1 



- ®J^ 



4 



t: 

1$ 





m 



es S/iu „ r _ _1 ► Vs/vv ^ 

*» "«" — N/W/v 




Generator Ao. / 



Generator //o-Z 



Fig. 266. — Early Type of Switchboard. 



centers are shown at the top of the board on each side. The posi- 
tive leg is connected to the positive bar by a single-throw switch 
through a fuse, and the negative leg is carried through a fuse to a 
terminal between the negative bar of the two machines. Here it is 



560 Naval Electricians' Text Book 

connected to a double-throw single-pole switch, by which either 
machine may be utilized to supply current to the section. To 
throw from one machine to the other, it is simply necessary to throw 
over the switch. 

The main bus bars are fused at their positive and negative ter- 
minals, these fuses carrying the whole current from the generators. 

To connect the machines in parallel, it is only necessary to con- 
nect the negative bars and the equalizer terminals, as the positive 
are permanently connected, and this is done by simply closing the 
double switch. 

If there are three generators, the only alteration in the switch- 
board is the addition of another negative bus bar, and a common 
equalizer bar at the bottom by which any combination of the three 
can be put in parallel. 

Instrument Boards. — As a part of this switchboard, on each side 
of it are installed boards, similar in construction to the main 
switchboard, containing the instruments for use with the generators. 
One of these contained a lamp ground detector, a voltmeter that 
could be connected to either set of bus bars by a shifting switch, 
and an ammeter for each machine in series with the main leads. 
The other board contained the voltmeters and ammeters for the 
search-light circuits, there being one of each for each search-light. 

The shunt field rheostats were placed conveniently below the 
main switchboard and the resistances of the search-lights near their 
instrument board. 

Switchboard for Small Vessels. 

A type of switchboard used on a few small vessels of the gunboat 
class is shown in Fig. 267. 

There are three horizontal bus bars, one positive, one negative 
and one equalizer bar. There are two vertical bus bars, one being 
connected to the horizontal positive bar and one to the negative bar. 
Connected to these vertical bus bars are horizontal section bars, one 
of each set connected to the vertical positive bar, the other to the 
vertical negative bar. The horizontal section bars are flat on the 
back of the board and also one horizontal bus bar ; the vertical bars, 
equalizer and one horizontal bus bar being raised from the board, 



Switchboards axd Distribution Paxels 



561 



the connections between them being made by threaded bolts. The 
connections are indicated by the small black squares. 

The positive, negative and equalizer switch for each generator 



Ins- 











+ 












+ 












+ 






iv^r- 


- 


1 





To St.. 



.Brush 
1 



Fig. 267. — Switchboard for Gun Boats. 



are all connected, one motion closing all three. The positive and 
negative section switches are connected and one motion closes or 
opens both. Each generator lead is protected by a fuse on the 
board and each leg of each circuit as represented. 



562 



Naval Electricians' Text Book 



A, A, represents the ammeters, one for each generator connected 
to an ampere shunt on the board. V is a voltmeter which is con- 
nected to indicate the voltage of either machine by means of the 
shifting switch. The same switch arrangement is used on the 
ground detector shown above the voltmeter. The leading wires for 
these instruments are connected to the switchboard terminals inside 
the main switches so they indicate when those switches are open. 

Below the switches and bus bars are shown the shunt field 
rheostats. 




Fig. 268. — Connections of Search-light Panel. 



If both machines are running they must run in parallel, for 
closing both main switches connects them so, at the same time con- 
necting the brushes of the machines through the equalizer. 

In this figure all the bus and section bars and leading wires are 
behind the board, the instruments, switches, switch clips, fuses and 
rheostat arms only showing on the front. 

Search-Light Panel. — In vessels of a size having such a designed 
switchboard it is usual- to install one search-light, a separate panel 
being used for the instruments as shown in Fig. 268. 



Switchboards axd Distribution" Panels 563 

The leads for the search-lights for each generator are taken 
from the switchboard terminals on the generator side of the main 
switches to contacts on the search-light panel. The search-light 
terminals are connected to the center contacts to which are attached 
a double-pole, double-throw switch, so the light can be supplied 
from either generator. One generator can be supplying current for 
lights, while the other is running the search-light, both running 
separately, the main switch of the generator on the search-light 
being open, or it can be closed when the two will run in parallel. 
One center contact is in connection with the variable resistance R, 
from which the current flows through the circuit breaker C, am- 
meter A, through the arc L and back to the other center contact. 
The voltmeter is connected to show the voltage at the lamp termi- 
nals, the drop from the generator voltage being due to the resistance 
R. In this panel only the instrument's circuit breaker and rheostat 
show on the face of the board, the leads and connections are on the 
back. The front view is shown. 

These two designs of switchboards will illustrate the general idea 
of what is expected of a switchboard, being more complex in its 
construction as the demands are greater. The method of distri- 
bution is again referred to under the subject, Wiring, showing 
plainly that what is sufficient for one class of ships may be totally 
inefficient for another. In present ships not only are there main 
switchboards but auxiliary ones, called distribution switchboards, 
situated near the extremities of the ship far removed from the 
generator-room. 

However the designs may differ, the requirements may be the 
same, and switchboards are now made under specifications of the 
Bureau of Equipment from which the following is copied : 

General Specifications. 

" The design of the switchboard in general to be such that any 
generator or any combination of generators operating in parallel 
may be run on any circuit or any combination of circuits. These 
circuits are search-light, light, power and one for each turret, the 
operation of whose electrical-turning mechanism requires a separate 
generator. 



5G-4 Naval Electricians' Text Book 

" For the larger installations the switchboard shall have a gen- 
erator panel, a lighting distribution panel, a power distribution 
panel and a search-light panel. The first three to be continuous 
and form one board. The last may be separated from the main 
board. 

"When the installation consists of two generating sets only, the 
lighting distribution panel, the power distribution panel and pos- 
sibly the search-light panel may be combined. Should the instal- 
lation consist of one generating set only, and that not larger than 
8 kilowatts the entire switchboard may be installed as one panel. 

" The switchboard is to be arranged for connecting the negative 
lead of each machine to a horizontal common negative bus bar by a 
single-throw, single-pole switch. 

"When generators are more than three in number, each one is 
to be arranged for connection to each of two horizontal equalizer 
bus bars by means of single-pole, single-throw switches. 

"To have only one equalizer bus when installation consists of 
three generators and a single equalizing switch when of two gen- 
erators. 

" To have a vertical bus bar for the positive leads of each gen- 
erator and a horizontal bus bar for each circuit, *. e., one for 
search-lights, one for lights and one for power. 

" At each crossing point of these two sets of bus bars, connection 
is to be made by means of single-pole, single-throw switches. 

" The arrangement of the generator panel to be such that all 
the switches and instruments necessary for the control of one 
generator shall be in a vertical line, and shall consist of (starting 
from top) a single-pole automatic circuit breaker, an ammeter 
shunt, an ammeter, handle for operating field regulator, voltmeter 
receptacle, such field-controlling switches as the turret system may 
require, positive generator switches connecting to circuit bus bars, 
switch to common negative bus bars, switches to equalizer bars and 
lastly a switch for shunting around the series field of generator 
when turret-turning system so requires. 

" Arrangement of voltmeters to allow the voltage of any gener- 
ator to be read on either of two voltmeters; to allow all the volt- 
meters to be interconnected for calibration* to allow the simulta- 



. Switchboards axd Distribution Panels 565 

neous reading of the voltage of as many generators as it may be 
desired to connect in parallel at any one time. 

" Light distribution panel to contain a double-pole switch, fused 
for each lighting circuit, a main negative lighting switch, and when 
a separate search-light panel is used the light distribution panel is 
to contain a main negative search-light switch. 

" Each search-light to have its own ammeter, double-pole auto- 
matic circuit breaker and regulating resistance. 

" Switchboard to be provided with a lamp ground detector with 
switch for breaking ground connection. In addition a voltmeter 
ground detector is to be provided with leads to assist in determin- 
ing circuit which the ground is on. 

" All circuits to terminate and all connections to be made on 
the back of the board." 

Standard Switchboard. 

The switchboard designed under the preceding specifications is 
the one now installed as the standard, and the following detailed 
description with accompanying figures will make its operation clear. 
This description is for a plant of eight generators and five circuit 
bus bars. 

This switchboard is adapted for use on board ships having two 
electrically-operated turrets, and in case it is used on ships which 
have no turrets, the general arrangement need not be changed, but 
all such switches and the like, as may be essential for turret turning 
only, should be omitted. 

The general arrangement is such as to allow any number or 
combination of generators to run on any circuit or any combination 
of circuits. These circuits are five in number, namely, search-light, 
lighting, power, forward turret turning and after turret turning. 

To accomplish this, the negative pole of each machine can be 
connected by a single-pole, single-throw switch to a horizontal com- 
mon negative bus bar, whereas there are eight vertical positive gen- 
erator bus bars, one for each generator. Back of these eight bars 
are five horizontal circuit bus bars, and where these two sets cross 
(5X8 = 40 points) there are single-pole single-throw switches 
which allow the positive leg of each, any or all generators to be con- 
nected to each, any or all circuits. 



566 Naval Electricians' Text Book 

For paralleling generators there are two separate equalizer bus 
bars, one for lighting and another for power (there will be no 
occasion for paralleling machines on search-light or turret-turning 
circuits) . Such generators as may be desired are connected to these 
equalizer bus bars by removable blade plug switches. 

When a generator is used to operate the turret-turning motors, 
the series field is short-circuited through a special German silver 
shunt, in addition to the shunt used on the generator itself. This 
is accomplished by single-pole single-throw switches at the base of 
board, one switch to each machine. 

Eef erring to Fig. 269, each of the generator panels is arranged 
in four vertical sections, each section containing all the apparatus 
necessary for the operation of its own generator. Starting at the 
top we have a single-pole automatic circuit breaker, connected in 
on the positive leg of the generator (handle of circuit breaker must 
be within 6 feet of deck), then the ammeter shunt (on back of 
board), then the ammeter and wheel for operating the field regula- 
tor, wheel connected to rheostat by sprocket chain. Next comes the 
plug receptacle for connecting to voltmeters, and then the field- 
control switches, three pairs of single-pole single-throw switches 
(description of last two devices follows later). Next come five 
single-pole single-throw positive generator switches by means of 
which the generator may be connected to (proceeding in order 
starting with the upper switch) 1st, search-light bus; 2d, light- 
ing bus ; 3d, power bus ; 4th, forward turret bus ; 5th, after 
turret bus. In the same vertical row but on lower panel there are 
four single-pole single-throw switches; the upper one connects the 
negative leg of the generator to the common negative bus bar, the 
two middle switches connect the equalizer bars, and the lower switch 
is to shunt the series field for turret turning, as previously 
mentioned. 

At the left of the generator panels is the power distribution panel, 
containing as many double-pole single-throw fused switches as may 
be required. Arranged at the top of this panel is a ground de- 
tector with receptacle, also two voltmeters, with plug receptacle 
underneath. In the center of the power panel is a main negative 
power switch, single pole, single throw, while on each side are two 



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Switchboards axd Distribution Paxels 569 

single-pole single-throw switches controlling the negative legs of 
the turret-turning circuits, the left-hand switch is for forward tur- 
ret and the right-hand switch for after turret. Again, outside of 
these last-mentioned switches are the field switches of the turret- 
turning motors and generator used for turret turning. These are 
double-pole single-throw switches with an extra set of long switch 
clips, across which is connected a field discharge resistance. 

To the right of the generator panels is the lighting distribution 
panel containing as many double-pole single-throw fused switches 
as may be required. At the top of this panel is an ordinary lamp 
ground detector, with a small single-pole single-throw switch to 
break the ground connection (this operation being necessary before 
using detector on power panel). This panel also contains two 
voltmeters with plug receptacle underneath. On lower panel are 
two single-pole single-throw main negative switches, one for lighting 
circuit and the other for search-light circuit. 

Each generator contains on its headboard a main fuse on the 
positive leg. 

All switches on generator panels are to throw horizontally, to 
be hinged on the generator end and throw to the left. For the for- 
ward turret, after turret, equalizers and series shunt, removable 
blade plug switches are to be used. 

Only four blades are supplied for each equalizer, and not more 
than two blades for each of the others, i. e., forward turret, after 
turret and series shunt. When a switch is open, the clip is to be 
plugged with a stop which will prevent accidental closing. 

The field-control switches allow three methods of field excita- 
tion. By throwing the two upper switches the machine is made 
self-exciting. By throwing the two middle switches the machine is 
separately excited and controlled from the forward turret. By 
throwing the two lower switches the machine is separately excited 
and controlled from the after turret. 

Voltmeter Connections. — The voltmeter connections, as shown in 
Fig. 271, are identical with but more clearly shown than in Fig. 
270. The plug receptacle on the power circuit panel and the four 
receptacles on the left-hand generator panel, i. e., for machines 
Nos. 1, 2, 3 and 4, have a spacing of 1 and 2 inches, whereas the 



570 



Naval Electricians' Text Book 



receptacle on the lighting panel and those for machines Nos. 5, 
6,. 7 and 8, have a spacing of 1^ and 2^ inches. By nsing the 1-inch 
plug on any receptacle on the generator panel the voltage of the 
machine is read on voltmeter No. 1, likewise by nsing 2-inch ping 
the voltage can be read on voltmeter No. 2. Similarly, on the right- 
hand generator panel the 1-J-inch ping throws voltmeter No. 3 across 
the generator terminals and the 2f -inch ping throws voltmeter No. 4 





RECEPTACLES A ARE FOR 1 <* 2 PLUGS 

do B' do do 1 Vx & 2'/i do 

ONLY ONE PLUG OF EACH SIZE IS SUPPLIED. 



r 




CENTERS Or RECEPTACLES 

CONNECT TO GENERATOR SIDE 

OF RESPECTIVE CIR CUIT- BREAKERS . 



^■common negative^* 

Fig. 271. — Voltmeter Connections on Standard Switchboard. 



across the terminals. Thns we can read the voltage of any two 
machines on the left-hand and of any two machines on the right 
panel (fonr machines in all) simultaneously. 

With the 2-inch plug in a receptacle on the generator panel and 
the 1-inch plug in the receptacle on the lower panel, we have volt- 
meter No. 1 in parallel with voltmeter No. 2 for calibration. 

With the 1-inch plug in a receptacle on the generator panel, the 
2-inch plug in the receptacle on lower panel, and the lj-inch plug 



Switchboards axd Distribution Paxels 571 

in the receptacle on lighting panel, voltmeter Xos. 1 and 3 are in 
parallel. By substituting the 2-J-ineh plug for the 1^-inch plug in 
the above arrangement Xos. 1 and 4 are in parallel. As only one 
plug of each spacing is furnished, it is imjDossible to make a short 
circuit or parallel two machines on the voltmeter connections. An 
inspection of Fig. 271 shows this to be true. 

Parallel Connections. — When starting up a new machine to be 
parallel with one already running the operation at the switchboard 
is as follows: 1st, close circuit breaker; 2d, close equalizer switch; 
3d, close switch to common negative; 4th, plug to voltmeter and 
adjust voltage by field regulator; 5th, and last, close positive switch. 

Ground Detectors. — For detecting grounds, the lamp detector on 
the upper part of lighting panel is connected permanently across 
the common negative bus and the positive leg on the lighting circuit 
panel ; and when using ground detector on power panel, the ground 
connection on this lamp detector must be broken. The connections 
to this ground detector (on power panel) are such that when a 
circuit is grounded on the positive leg, the instrument will indi- 
cate when plugged to negative, and for a ground on the negative of 
any circuit the instrument will indicate when plugged to any of 
the positive circuit bus bars, provided of course that said bar is 
alive, and here it should be noted that a bar is alive when any 
switch in the horizontal row connecting to it, is thrown. 

To locate a ground in the quickest possible manner the group 
switches, i. e., main negative and positive generator switches on 
the lighting circuit should be opened; if the ground still appears, 
these switches should be closed and the corresponding switches on 
each circuit opened (one circuit at a time) until the ground disap- 
pears. When the ground is singled down to one group, the circuit 
switches on this group should be opened one at a time until the 
defective circuit is found. 

In Fig. 269, the circuits marked lighting circuits, power circuits 
and search-light may lead to other distribution boards in different 
parts of the ship, so all the lights or power required for one locality 
may be controlled independently of the main switchboard. Those 
marked to forward turret and to after turret lead to panels conve- 
nient to those places where are installed the necessary switches and 
instruments for the proper control of the current. 




Fig. 272. — Connections of Dynamo Room Switchboard 



574 



Naval Electricians' Text Book 



Distribution Boards. 

Since the adoption of the standard specifications for switch- 
boards given in the preceding sections, other forms of switchboards 
have been installed to meet the requirements for larger power. In 
some late ships there are two distinct dynamo-rooms with a dynamo- 
room board in each room, from which current is distributed to two 
distribution boards situated in separate parts of the ship. Each 
dynamo-room can supply each or both of the two distribution 
boards, and from these latter boards, current is distributed 
throughout the ship for the various purposes of lighting or power. 

The diagrammatic sketches of the dynamo-room board and distri- 
bution boards as installed on the North Carolina and Montana are 
shown in Figs. 272 and 273. 

From the general description of the standard board previously 
given and with the help of the accompanying list of reference parts, 
the connections can be easily traced. 



Dynamo-Room Board. 

1. Power Mains to Starboard Distribution Board. 

2. Power Mains to Port Distribution Board. 

3. Lighting Mains to Starboard Distribution Board. 

4. Lighting Mains to Port Distribution Board. 
5, 6, 7. Generator Voltmeters, 150 volts. 

8, 9, 10. Generator Ammeters, 1200 amperes. 
11, 12, 13. Generator Field Eheostats. 

14. Calibrating Voltmeter. 

15. Calibrating Voltmeter Switch. 

16. Bristol Eecording Ammeter, 500 amperes. 

17. Bristol Eecording Ammeter, 3500 amperes. 
18, 19, 20. Positive Lighting Bus Switches. 
21,22,23. Positive Power Bus Switches. 
24,25,26. Negative (Common) Bus Switches. 

27, 28, 29. Equalizer Switches. 



Switchboards and Distribution Paxels 575 

Distribution Boards. 

1. Power Mains from Port Dynamo-Room. 

2. Power Mains from Starboard Dynamo-Room. 

3. Lighting Mains from Port Dynamo-Room. 

4. Lighting Mains from Starboard D} T namo-Room. 

5. Turret Power Switch from either Starboard or Port 

Dynamo-Room. 

6. Power Switch from either Starboard or Port Dynamo- 

Room. 

7. Lighting Switch from either Starboard or Port Dynamo- 

Room. 
8-8. Double-Pole Circuit Breakers. 
9-9. Single-Pole Circuit Breakers. 

10. Power Mains to Forward 12-Inch Turret. 

11. Power Mains to After 12-Inch Turret. 
12-12. Power Mains to 8-Inch Turrets. 

13. Power Mains. 

14. Search-Light Switches. 

15. Ammeter for Total Turret Power. 

16. Ammeter for Total Power. 

17. Turret and Power Voltmeter. 

18. Voltmeter Ground Detector. 

19. Lighting Voltmeter. 

20. Total Lighting Ammeter. 

21. Search-Light Voltmeter. 
22, 22, 22. Search-Light Ammeters. 

23. Lighting Mains. 

24. Turret Lamp Ground Detector. 

25. Power Lamp Ground Detector. 

26. Turret, Power and Lighting Lamp Ground Detector. 

27. Search-Light Rheostats. 

28. Search-Light Mains. 

29. Voltmeter Ground Detector Switch. 
F Fuses. 

L Lamps. 



28 I * 28 | i 28 




If 




FI0 . 2I3 .^*°^ of Distribution Board. 



CHAPTER XXIV. 
INCANDESCENT LAMPS. 



■ 



When a current of electricity is urged through a conductor, heat 
is developed, the amount of heat being proportional to the amount 
of energy expended in the conductor. If a current C is forced 
through a resistance R for a time t, the number of joules, or electri- 
cal units of heat developed, is C 2 Rt. 

The distinction between heat and temperature must be kept in 
mind. The same amount of heat may be applied to two conductors, 
and the resulting temperature be widely different. When a con- 
ductor is made very hot, or has a high temperature, it becomes 
luminous and the luminosity is proportional to the temperature. 
Suppose there were two conductors A and B of same sectional area, 
and B twice as long as A, and therefore twice its resistance, and 
equal currents urged through both. The energy expended in A, or 
the heat developed will be only half that in B, but the temperatures 
will be equal, as B has twice as much matter as A. The luminosity 
of these two conductors will be the same, although B absorbs or 
requires twice as much energy as A. Suppose, however, the con- 
ductors are the same length, but B is given the same resistance as 
before by halving its cross-sectional area. With the same currents 
as before, B still absorbs twice as much energy as A, and twice as 
much heat will be developed in B as in A. Since the mass of B is 
only one-half that of A, equal quantities of heat would cause the 
temperature of B to be twice that of A, and since twice as much 
heat is developed in B, its temperature is raised to four times that 
of A, and therefore its luminosity is four times as great for the 
same current. 

This shows that to obtain great luminosity a large amount of 
energy must be expended on a small mass of matter, and the 
mass must be kept small by reducing the area of cross-section 
rather than by increasing its length and the material should have 
a high specific resistance. Enough heat may be absorbed by a con- 



INCANDESCENT LAMPS 579 

ductor of small mass to raise its temperature to such a degree that 
it may become luminous, and if the heat produced by the current is 
not radiated as fast as produced, the temperature will reach the 
melting point, and the conductor, or portion of it, will be destroyed 
by uniting with the oxygen of the air. If the conductor was heated 
to incandescence before burning up and it could be kept in such a 
state, then we would have an incandescent lamp. 

To prevent its uniting with oxygen, the resistance of an ordinary 
incandescent lamp is secured in a glass bulb from which almost all 
air and other gases have been exhausted. 

Manufacture of Lamps. 

The materials which have been tried in the incandescent or glow 
lamp are platinum, osmium, iridium, an alloy of platinum and 
iridum, carbide of titanium, tantalum, tungsten and carbon. Of 
these, carbon is the substance almost universally employed, its chief 
advantages being : ( 1 ) That after the temperature of incandescence 
is reached, the luminous rays increase more rapidly than the heat 
rays for further increases of temperature than is the case with 
metals. (2) Its temperature of volatilization is higher than that of 
metals. The temperature at which metals emit light is not much 
less than their melting points, while carbon has no actual melting 
point, but a temperature of volatilization higher than that needed 
for incandescence. (3) The cross-sectional area of carbon can be 
made more nearly uniform than is possible with metal wires. 

The complete manufacture of an incandescent lamp requires 
from thirty to forty distinct operations, the principal of which are 
given in the following description : 

The filament is the chief feature of all glow lamps and upon its 
manufacture depends the success and behavior of the completed 
lamp. In nearly all cases, the filament is made from cellulose, a 
transparent, gelatinous hydrocarbon. This cellulose is prepared 
in different ways as follows : 

1. Treating pure cotton wool to a washing and boiling operation 
to remove any " dressing," dirt or foreign material obtained in the 
course of its manufacture. After drying, the wool is wound loosely 
around two opposite sides of a rectangular glass frame of such a 



580 Naval Electricians 5 Text Book 

size that each ply is a little longer than the length of the completed 
filament. The cotton thus wound is immersed in a clear solution 
of pure concentrated sulphuric acid and pure water of proportions 
2 to 1. This operation only takes a short time and is complete 
when the last traces of the strands of cotton disappear, after which 
the frame is immersed in clear running water. It is next immersed 
in a one per cent solution of ammonia and water to remove all 
traces of acid and again washed in clear water. The cotton has 
been transformed into the transparent, gelatinous substance known 
as cellulose. 

2. The purest cotton wool is heated with a solution of zinc 
chloride in which it dissolves, forming a syrupy mixture from which 
is precipitated by alcohol a hydrated cellulose zinc oxide. The 
solution is treated with hydrochloric acid which liberates the zinc, 
after which it is washed and the solution is reduced to cellulose by 
ammonium sulphide. The fluid result is a brownish liquid of about 
the consistency of molasses. 

3. Special kinds of paper are chemically treated in such a way 
as to produce a thick solution of cellulose. 

Forming the Filament. — After the thick gelatinous mass of cellu- 
lose has been obtained, the desired form of the filament is made 
while it is still in a pliable condition. The solution is forced by 
light pneumatic pressure through orifices or dies, made of sapphire- 
agate stones which contain holes of diameters corresponding to the 
area of cross-section desired. The cellulose issues from these holes 
in a continuous thread and is allowed to coil in glass jars filled with 
alcohol which acts to set and harden it. This thread is allowed to 
remain until all traces of the zinc chloride disappear when the 
thread now resembles fine cut catgut and is tough and flexible. It 
is washed well to remove all traces of chemicals and is then ready 
for shaping. 

The filaments are shaped by winding the thread over " formers " 
of carbon, according to the desired shape of the completed filament. 
These are then lightly baked to ensure the shape being retained. 
Such a shape is shown in 2, Fig. 274. 

Carbonizing the Filament. — After forming, the thread is re- 
moved from the formers and is closely packed with powdered carbon 



Incandescent Lamps 581 

in graphite crucibles. These crucibles are then placed in a coke 
furnace and brought gradually to a white heat, at which tempera- 
ture they are kept for a day or two when they are allowed to slowly 
cool. This operation converts the threads into pure carbon of a 
dull black color. The threads are then measured for diameter by 
micrometer calipers, measuring to towo" i ncn an ^ sorted according 
to diameters. 

The next step in the process of manufacture is the flashing pro- 
cess, and the arrangement for doing this varies in different factories. 
In general it consists in raising the filament to a high degree of 
incandescence while it is an atmosphere of some hydrocarbon vapor 
such as gasoline or benzine. The thinner portions of the filament 
become hotter than the rest which causes the carbon in the vapor 
to be deposited in greater quantity at those points, as well as in 
every little hole in the filament, and thus causing the filament to 
become of uniform cross-section throughout. 

In some processes, the filament is hung in an air-tight vessel 
containing the hydrocarbon, which vaporizes and surrounds the 
filament ; in others, the vessel is fitted with two orifices, by which 
air may be exhausted from one and vapor admitted at the other. 
This method insures the rapid volatilization of the liquid hydro- 
carbon. While surrounded by the vapor, the filament is connected 
either to a generator or a storage battery and heated to incan- 
descence, the operation being repeated several times. As the carbon 
is deposited the resistance decreases and the current increases, and 
automatic arrangements are made by which the current is shut off 
when the desired resistance has been attained. 

The color of the filament has now changed to a steel gray and is 
coated uniformly with finely divided, hard and compact carbon. 
It is now ready for connection to the plug. 

Small copper wires, such as shown in 1, Fig. 274, are attached 
to two platinum wires, each about \ inch in length, by heating and 
fusing the two together. This combination of wires is then 
assembled in a glass tube (3, Fig. 274), the platinum wires being 
fused in the glass (4, Fig. 274). Platinum is used because it 
does not fuse at the temperature necessary for fusing the glass, and 
its coefficient of expansion is about that of glass, so there is no 



582 



Naval Electricians' Text Book 



danger of leakage of air into the exhausted bulb due to unequal 
expansion. 

The filaments are then attached to the platinum wires by a 
carbon paste or cement which is carbonized by passing a current 
through the filament. The completed filament is shown at 5, Fig. 
274, and is then ready for attachment to the glass bulb. 

The Bulb. — There are no peculiarities in the construction of the 
bulbs, which are blown to the proper size and shape (7, Fig. 274). 






D 







Fig. 274. — Stages of Lamp Assembly. 



The glass tube holding the filament is secured in the mouth of the 
bulb and the edges are fused to the edge of the bulb (8, Fig. 274). 

Exhausting the Lamp Bulb. — It is of the utmost importance to 
secure a good vacuum inside the bulb, for the efficiency as well as 
the life of a lamp depends upon the goodness of the vacuum. The 
poorer the vacuum the greater the conduction of heat from the fila- 
ment to the bulb and to the outside atmosphere, so that the energy 
absorbed by the filament is not given as temperature to the filament 
and the efficiency is reduced. 

The life is shortened due to the disintegration of the filament 



Incandescent Lamps 583 

which is made manifest by the blackening of the inside of the bulb 
by the deposition of carbon on it. 

The bulb is connected to an air-suction pump, as the Sprengel 
mercurial pump. When the vacuum has attained a steady value, 
current is sent through the filament so as to heat it to redness and 
gradually increased to about 25 per cent above the normal incan- 
descence. This drives out any air that may be held in the filament, 
the pump kept going all the time. When the desired vacuum has 
been attained, the glass tube blown in the bulb and by which it is 
connected to the tube leading to the pump is gradually heated near 
the bulb until the glass softens. The bulb is gradually pulled away 
and the softened glass of the tube draws together and gradually 
closes the opening and a final twisting motion seals the bulb leav- 



a 







Fig. 275. — Types of Filaments. 



ing the little sharp nipple seen on all glow lamps. The lamp as 
now completed is shown in 9, Fig. 274. 

The Base Attachment. — The standard Edison base consists of a 
threaded brass open-ended cylinder, perforated with a hole near the 
middle of its length, and of a brass disc perforated through its 
center. The copper leading-in wires of the completed combination 
shown in 9, Fig. 274, are threaded through the holes, one in the 
cylinder and one in the disc. The whole cylinder is then filled 
with plaster of paris and when this sets, the ends of the wires are 
trimmed off and soldered at the perforations. 

In a method using a glass plug in place of plaster of paris, the 
plug is made of molten glass poured in the base, after which the 
contact is secured by a rivet. The other leading wire is soldered 
at the top of the base. 

The types of filaments used in naval incandescent lamps are 
shown in Fig. 275, and the lamps with which they are used are 
given in the table on page 588. 



584 Naval Electricians' Text Book 

Candle-Power of Incandescent Lamps. 

Lamps are rated and marked at so many candle-power, the stand- 
ard now nsed in the service being 1, 2, 5, 6, 10, 16, 32 and 150 
candle-power. For ordinary illumination 16-candle-power lamps 
are nsed, those of 5 candle-power being nsed in store-rooms and pas- 
sages below decks, those of 32 candle-power in the night signal sys- 
tem, running lights, truck lights and anchor lights, and those of 150 
candle-power for general illumination in open spaces, where a large 
amount of light is needed for night purposes and in the diving 
lamp — these generally being used in portable fixtures. Lamps of 
1, 2, 5 and 10 candle-power are used in instruments and telephotos, 
and the 6 candle-power for torpedo lamps. 

Standard Lamp. — A 16-candle-power lamp is one that will give 
the same intensity of light, or the same amount per unit of area as 
sixteen standard candles, or an intensity sixteen times as great as 
one standard candle; a standard candle being a spermacetic candle 
J of an inch in diameter, burning 120 grains per hour. The practi- 
cal unit of white light is the quantity of light emitted normally by a 
square centimetre of surface of molten platinum at the temperature 
of solidification. 

Comparison of Lights. — Incandescent lamps are compared with a 
standard candle by means of photometers, these being instruments 
by which the amount of light falling on a given surface may be 
measured, or by which the effect of light from two sources is neu- 
tralized, and the intensities of the two lights compared. The in- 
tensity of light from a given source is determined by the physical 
law, that the intensity of light received by an object varies inversely 
as the square of its distance from the source of light. 

All lamps have marked on them the voltage necessary to pro- 
duce the rated candle-power. A lot of lamps made at the same 
time, by the same process and by the same workmen with the same 
care will not all give the same candle-power for the same voltage. 
Instead of considering the voltage constant and determining the 
candle-power, the candle-power is regarded constant, and the volt- 
age necessary to produce that candle-power is determined and 
marked on the lamp. Lamps are tested for candle-power in con- 
nection with the photometer in a horizontal position, that is, the 






Incandescent Laz\ips 585 

lamps themselves hang vertically with the loop of the filament 
opposite and on a level with the spot on the photometer to be 
illuminated, and the candle-power thus obtained is called the hori- 
zontal candle-power. As the candle-power thus obtained would be 
different from that determined in any other position, it is necessary 
to find what is called the mean or average spherical intensity of the 
illumination. 

The mean spherical candle-power is the average candle-power 
on the interior surface of a sphere, of which the source of light is 
the center. 

Effect of Age on Candle-Power. — When a lamp is first connected 
to a circuit, the candle-power increases for a time and then begins 
to fall, reaching the initial candle-power at the end of about 100 
hours' burning, and the decrease in candle-power is steady from that 
time. As the efficiency rises, the candle-power falls more rapidly. 
A lamp absorbing 3.5 watts per candle-power will fall to about 75 
per cent of its candle-power at the end of 900 hours, and one 
absorbing 2.5 watts will fall to the same percentage at the end of 
about 300 hours. 

As a lamp gets old and its candle-power and efficiency fall, it is 
much better after a certain point to throw it away than to continue 
to burn it till rupture takes place. 

Over and Under Running. 

As far as possible all lamps should be worked at the voltage which 
will give their rated candle-power. The voltage that a lamp will 
require is determined by the dimensions of the filament, and each 
filament is so constructed as to yield its standard candle-power at 
the highest temperature, about 2000° C, compatible with dura- 
bility, and much increase of temperature would probably cause 
rupture of the filament. A very slight increase in the voltage pro- 
duces a much greater per cent increase in luminosity, but a corre- 
sponding danger of rupture. The candle-power increases much 
faster than the voltage and experiments seem to show that the 
candle-power of a given lamp varies as the sixth power of the 
applied voltage or as the cube of the absorbed watts. When the 
candle-power is reduced one-half the power absorbed in the filament 
has only fallen about 20 per cent. 



586 Naval Electricians' Text Book: 

This consideration shows that by under running a generator, that 
is running at a lower speed and consequently at a lower voltage than 
the normal, no advantage is gained. Even a reduction of 2 per 
cent in the normal voltage makes itself very apparent in the amount 
of light emitted, and while it may act to prolong the life of a lamp 
the effect is neutralized by the reduced efficiency, more power being- 
required to produce the candle-power as the voltage falls. 

The effect of over running is to seriously lessen the life of lamps, 
an increase of 3 per cent in the voltage being sufficient to reduce 
the life of a lamp to one-half, and an increase of 6 per cent to 
one-third. 

Efficiency of Incandescent Lamps. 

The efficiency of a lamp is the ratio of the mean spherical candle- 
power to the electrical power absorbed in producing it, but is 
usually referred to as so many watts per candle-power. If a 16- 
candle-power lamp absorbed 56 watts, its efficiency would be spoken 
of as 3.5 watts, that is 56 -=- 16, its efficiency being -|~f = .286. 
The electrical power absorbed is obtained by properly connecting up 
an ammeter and voltmeter in the lamp circuit when testing it for 
candle-power in the ^photometer, the product of the volts and 
amperes giving the total watts absorbed. The electrical horse- 
power spent on a lamp is equal to the number of watts absorbed by 
the lamp divided by 746. The number of heat units or calories 
given out per candle-power is found by multiplying the number of 
watts absorbed by .24 and dividing by the number of candle-power. 

The question of efficiency is closely connected with the candle- 
power and life of a lamp. High efficiency means high voltage, 
high candle-power and high temperature and consequent economy 
but at the expense of short life, while a reduced efficiency means 
less economy and longer life. A lamp that is burning at a reduced 
candle-power yields a lower efficiency but lasts longer than one of 
the same type at the full power, but it is more economical to run 
lamps at a high than at a low efficiency. The average life of 
initially high efficiency lamps is short and they deteriorate rapidly 
in candle-power and efficiency after about 200 hours' burning. 



IXCAXDESCEXT LjAZUPS 



58 r 



Standard Incandescent Lamps. 

The lamps manufactured for the use of the Xaval Service must 
conform in dimensions and shapes to certain standards, these being 
shown in Fig. 2TG. 

The bases for the 100, 32, 16 and 10 candle-power are of the 
standard form Edison base, that for the 5 candle-power is of the 




Fig. 276. — Standard Lamp Shapes. 



candelabra form of Edison base. The base of the 6-candle-power 
torpedo lamp is fitted with leads as shown in the figure. 

The bases are fitted with porcelain or glass buttons, forming the 
insulation between the contacts. These buttons are designed so 
that it is only necessary to make one channel through the button 
and this passes through the center of the button for the purpose of 
permitting the attachment of one of the lea ding-in wires to the 
contact in the center of the base. The base is firmly and accurately 



588 



Naval Electricians' Text Book 



fitted to the bulb with moisture proof cement. The leading-in wires 
and anchors are fused in the glass. These last are metal pieces 
secured to the loop to strengthen it and to prevent the loop from 
drooping when used in a horizontal position. 

The filaments are centered in the bulb and in the case of the 32, 
16 and 10-candle-power telephotos and 6-candle-power torpedo 
lamps are anchored. 

Each lamp is marked to the nearest even volt that is necessary 
to give its rated candle-power. 



1 


2 


3 


4 


5 


6 


7 


8 


9 


Class. 


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Special Lamps. 
Instrument. 

1 c.-p., 10 volts, clear 

3 c.-p., 80 volts, clear 

2 c.-p., 110 volts, clear — 
2 c.-p., 233 volts, clear. . . . 

Torpedo. 

6 c.-p., 80 volts, clear 

6 c.-p., 110 volts, clear — 
6 c.-p., 123 volts, clear 

Telephotos. 

10 c.-p., 80 volts, clear 

10 c.-p., 110 volts, clear. . . 
10 c.-p., 123 volts, clear. . . 

Regular Lamps. 
Regular. 

6 c.-p., 80 volts, clear 

5 c.-p., 110 volts, clear — 
5 c.-p., 123 volts, clear — 


1 

3 
3 

3 

6 
6 
6 

10 
10 
10 

5 
5 
5 
16 
16 
16 
16 
16 
16 
33 
32 
32 

150 
150 
150 


4.9 
11 
13 
13 

30 
30 
30 

36 
36 
36 

19.5 

19.5 

19.5 

56 

56 

56 

56 

56 

56 
115 
115 
115 

465 

465 

465 




9.35-10.75 

78- 84 
106^116 
119-139 

77- 85 
106-116 
119-139 

75- 83 
104-113 
119-137 

77- 83 
105-113 
119-127 

77- 83 

78- 83 
107 112 
108-113 
121-125 
122-126 

76- 82 
106-112 
120-126 

76- 82 
106-113 
130-126 


4.5- 5.3 

10.1-11.9 

12-14 

12-14 

37-33 
37-33 
37-33 

34-38 
34-38 
34-38 

18-21 
18-31 

18-31 

53.3-58.8 
53.3-59.8 
53.3-58.8 
53.3-59.8 
53.3-58.8 
53.2-59.8 
109 121 
109 121 
109-121 

443-488 
443-488 
443-488 


553 

1,388 
1,473 
1,473 

138 

138 
138 

3,680 
3,680 
3,680 

3.760 
1,150 
1,150 
13,000 
13,000 
13.000 
13,000 
13,000 
12,000 
30.000 
30,000 
30,000 

13,800 
20,700 
30,700 


68 
93 
55 
55 

15.4 
15.5 
15.4 

1,840 
1,840 
1,840 

930 

368 
368 


2.0? 


Double loop 
3-coil spiral 
....do 

Loop 


4.79 

6.1 

6.1 

13.5 


do 


13.5 


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Oval 


13.5 
12 6 


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2-coil spir 
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al 


13.5 
12.5 

7.14 
7.14 

. 7.U 


16 c.-p., 80 volts, clear 


Oval 




8,000 19 
8,000: 19 
8,000 i 19 


16 c.-p., 80 volts, frosted.. 
16 c.-p., 110 volts, clear 


....do. ... 
....do 




16 c.-p., 110 volts, frosted. 
16 c.-p., 123 volts, clear. - . . 
16 c.-p., 123 volts, frosted. 
32 c.-p., 80 volts, clear 
32 c.-p., 110 volts, clear . . . 
32 c.-p., 123 volts, clear . . . 

Diving. 
150 c.-p., 80 volts, clear . . . 
150 c.-p., 110 volts, clear . . 


....do.... 
. . . . do. . . . 
....do.... 
....do 




8,000' 19 

8,000 19 

8,000! 19 

11,000 40 


....do. ... 
.... do 




11,000 
11,000 

13,800 

20,700 


40 
40 


2-coil spiral 


150 
150 


150 c.-p., 123 volts, clear . . 


...do 


20,700 


150 



INCANDESCENT LAMPS 



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590 Naval Electricians' Text Book 

Tests. 

Lamps are tested for the purpose of determining the initial 
voltage, the total watts expended at the rated candle-power, the 
physical characteristics of the lamps and for life. The require- 
ments as to electrical qualifications are given in the table on 
page 589. 

Physical tests require an examination of the bases, filaments and 
'the vacuum; loose bases, spotted or discolored filaments or a poor 
vacuum being sufficient to reject them. 

From each quantity of lamps submitted for test, 10 per cent, 
known as the test quantity, shall be selected at random for test for 
the purpose of determining the mechanical and physical character- 
istics of the lamp, the individual limits of candle-power and watts 
per lamp and the life and candle-power. 

If 10 per cent of the test quantity show any physical defects, the 
entire lot may be rejected without further test. 

When tested at rated voltage, the test lamps shall not exceed the 
limits given in the schedule. If 10 per cent of the test lamps is 
found to fall beyond the limits stated, the entire lot may be 
rejected without further test. 

Unit of Candle-Power. — The unit of candle-power is the candle 
as determined by the Bureau of Standards at Washington, D. C. 

Photometric Measure. — The basis of comparison of all lamps is 
the same spherical candle-power. The nominal candle-power is the 
mean horizontal candle-power of lamps having a mean spherical 
candle-power value of 82.5 per cent of the mean horizontal candle- 
power. This is the standard value for filaments of the oval 
anchored type, other type filaments having a different percentage 
value. 

Life and Candle-Power Maintenance. — Life tests are made as 
follows : From each accepted package of lamps two sample lamps 
are selected which approximate most closely to the average of the 
test quantity. One of the two lamps thus selected will be sub- 
jected to a life test and designated as the life test lamp, the second 
or duplicate lamp being reserved to replace this test lamp in case 
of accidental breakage or damage during the life test. The test 
lamps are operated for candle-power performance at constant poten- 



Incandescent Lamps 591 

tial, average variations of voltage not to exceed one-fourth of 1 per 
cent, either side. The voltage for each lamp shall be that corre- 
sponding to an initial specific consumption of 3.76 watts per mean 
spherical candle, or, if tested upon a different basis, the results shall 
be corrected to a basis of 3.76 watts per mean spherical candle. 

Headings for candle-power and wattage are taken during life at 
the marked voltage of the lamps at approximately 50 hours, and at 
least every 100 hours afterwards until the candle-power shall have 
fallen 20 per cent below the initial candle-power, or until the lamp 
breaks, if within that period. The number of hours the lamp burns 
until the candle-power has decreased to 80 per cent of its initial 
value, or until the lamp breaks, is known as the useful or effective 
life. 

The average candle-power of lamps during life shall not be less 
than 91 per cent of their initial candle-power. In computing the 
results of test of a lot of lamps the average candle-power during life 
shall be taken as the arithmetical mean of the values for the indi- 
vidual lamps of the lot tested. 

Accurate recording voltmeter records are obtained during the 
test on lamps to show the average variation on the circuit. 

When so tested the lamps shall average at least the values for 
useful life given in the table. 

Illumination. 

Illumination is the amount of light falling upon some unit of 
area, as a square foot, of the surface to be lighted and is independ- 
ent of the nature of the surface, and the light may be either 
reflected, absorbed or transmitted. The illumination depends upon 
(1) the quantity of light from the source and (2) the distance be- 
tween the body illuminated and the source. The unit of illumina- 
tion generally accepted is the candle foot, being that amount of 
light falling upon a body at a distance of one foot from a standard 
candle. The intensity or amount of light per unit area also varies 
inversely as the square of the distance from the source of light. 
The question of the kind and location of incandescent lamps for 
ordinary ship's illumination is one that presents few difficulties, 
but one that creates at times considerable criticism. One candle 



592 Naval Electricians' Text Book 

foot is a convenient illumination for reading. For the ordinary 
heights on shipboard, one 16-candle-power lamp will illuminate well 
about 50 square feet of surface. As a matter of efficiency, pure 
and simple, that is to get the greatest amount of light from a given 
j^ower, it would appear that all lamps installed should have naked, 
clear glass bulbs; but other questions than efficiency, especially on 
shipboard arise, such as personal taste, structural details and the 
effect on the eye in reading, writing or working. 

For lighting in cabins and state-rooms, it is usual to use frosted 
globes, these being necessary for comfort and appearance even 
though some of them absorb even as much as 60 per cent of the light 
emitted. This loss of light seems a great waste, but not as much 
perhaps, as would seem on first glance. The filament in a frosted 
globe is invisible and the whole bulb looks as though it were the 
source of light, and the luminous area being thus enlarged, there 
is less contrast between the source of light and the objects lighted. 
In reality, the frosted globe is a better dispenser of light than the 
clear globe, each little particle of the rough glass acting as a prism, 
refracting the rays in all directions. A room with a naked gas 
flame appears poorly lighted compared to the same flame surrounded 
by a globe although the light emitted is certainly less in the latter 
case. It is often a question whether for reading or desk work a 
clear bulb high up or a frosted one low down will give the best 
results ; the amount of light received being not far from the same 
in both cases; the clear one losing in intensity due to its distance 
away. It seems perfectly proper not to use clear globes when they 
come within direct and constant range of the eye, as the pupil of the 
eye will involuntarily contract at the dazzling light, and it is doubt- 
ful if more rays actually enter the eye than in case of the frosted 
globe. 

Overhead lighting seems to be best adapted for ships' use for 
standing lights in open spaces where men are not berthed and side 
lighting where they are. In store-rooms and passageways, it is 
usual to place the lights where they are least in the way of movables, 
general illumination only being required. 

Simply as a matter of illumination and uniform distribution of 
light, a small number of low candle-power lamps is better than one 



Incandescent Lamps 



593 



lamp of the combined candle-power, thus four 16-candle-power 
lamps would give a better general effect than two 32's, although no 
more power is absorbed. 

The question of color of sides or ceiling of a room has consider- 
able to do with the lighting effect. Dull and dark surfaces absorb 
as much as 80 per cent of the light incident on them, while clean, 
white surfaces will reflect that much, adding to the general effect. 
With fairly white walls, a rule which allows two watts for every 
square foot of floor area, is one that would give more than ample 
illumination. 



Tantalum and Tungsten Filaments. 

The conductivity of metals is very much higher than that of 
carbon and several varieties of metal filaments have been used in 
lamps of recent manufacture. Owing to the high 
conductivity, the use of a long wire of small 
diameter is necessary and a filament of tantalum 
presents the unusual appearance shown in Fig. 
277. With ductile metals as tantalum such a 
filament is comparatively easy to make, but with 
non-ductile metals like tungsten, the method is 
not so simple. 

To make a tungsten filament, a carbon filament 
is first made which is electroplated with metallic 
tungsten. This is then -flashed in an atmosphere 
of hydrogen at very high temperature which re- 
sults in the absorption of the tungsten by the 
filament and the production of carbide of tungs- 
ten. The carbon is removed by heating the fila- 
ment to a high temperature while it is surrounded 
with tungsten oxide. The carbon oxidizes and 
passes off leaving the metallic tungsten filament. 




Fig. 277. 
The Tantalum 

Filament 

Incandescent. 

Lamp. 



The Nernst Lamp. 

Although the Xernst lamp has not been used in the naval ser- 
vice, it is of interest on account of the principles involved in its 
construction and of the high efficiencies obtained. 



594 Naval Electricians' Text Book 

This lamp differs from the ordinary incandescent lamp in that it 
is not enclosed in a vacuum, and instead of the filament being made 
of carbon, it is made of some highly refractory oxides " rare earths/' 
such as zirconia, thoria or yttria, made in the form of little rods 
and mounted on platinum wires by means of a paste of the re- 
fractory oxides. The lamp is operated in air and is only protected 
by the very high melting point of the filament. This filament is a 
non-conductor when cold but becomes a conductor when heated and 
its resistance decreases as the temperature increases. This is cor- 
rected by a stead}dng resistance in series with the filament, and 
including this resistance, the efficiency varies from .8 to 1.8 watts 
per candle-power. The steadying resistance is enclosed in a glass 
tube from which the air has been exhausted to protect the wire 
from oxidation. 

In order to make it conducting, the temperature is raised by 
what is called a heating resistance in shunt with the filament and 
close to it. The heater consists of one or more clay tubes wound 
with high resistance and covered by fire-clay. When the filament 
commences to conduct, a cutout disconnects the heater. 

This lamp finds its greatest application for outside illumination, 
though with frosted globes it is very satisfying for large interior 
spaces. 



CHAPTER XXV. 
ARC LIGHTS. 

The arc light is the oldest form of electric light known. Until 
recently it found no practical use for lighting on shipboard but now 
it is used in large spaces for general illumination as in the engine- 
rooms of large modern vessels. The application of the arc light to 
the focus of a reflecting minor, spherical or parabolic, in an 
enclosure to give a beam of reflected light gives the search-light. 

General Principles. — If two carbon points, forming part of a 
closed circuit in which a current is flowing, be separated a short 
distance and the current is strong enough, a spark will jump from 
one to the other. If the current continues steady and strong 
enough, a series of sparks will continue to jump from one to the 
other and if the distance between them is not too great, a flame will 
soon form, and this flame gives out light and heat. The explana- 
tion is as follows: The current passing from one carbon to the 
other is suddenly arrested when the carbons are separated, or more 
properly speaking, the current meets with a greater resistance, 
that of the air between the points, and the first spark is due to the 
high E. M. F. of the momentarily self-induced current. The cur- 
rent continues to flow through this high resistance, the result of 
which in a short time is to heat it; that is the air gap, to such a 
degree that it becomes incandescent. 

The incandescent flame produced between the points of the car- 
bons has a violet appearance, and from the fact that the original 
source of E. M. F. was a voltaic battery, it is commonly called the 
" voltaic arc/' The word arc is a corruption of " arch," which was 
originally used to designate the shape of the flame. 

Production of the Arc. — The operation of producing an arc by 
first bringing the carbons in contact and then separating them is 
commonly known as " striking the arc." The reason for this pre- 



596 Naval Electricians' Text Book 

liminary contact is that it would require a much greater E. M. 
F. in the circuit to start an arc across even the thinnest filament of 
air between the carbons. When the carbons first touch and current 
flows between them, the junction gets very hot owing to the resist- 
ance of the imperfect contact and when separated, the heat 
volatilizes some of the carbon and lowers the resistance sufficiently 
to allow the current to continue to flow. 

Electrodes. — The choice of electrodes used with the arc is practi- 
cally limited to carbon in some form or other. The intensity of 
light depends on the temperature at which volatilization takes place, 
and most metals have a low temperature of volatilization compared 
with carbon, and their temperatures of incandescence are very near 
their melting points. Carbon cannot be melted into a liquid state, 
but passes direct from the solid into the gaseous state, or volatilizes, 
only at a very high temperature. 

Form and Temperature of Arc. — The result of the great heat 
formed in the arc is to heat the carbon the current leaves, the posi- 
tive carbon, and this heat produces a carbon vapor that is projected 
across to the negative carbon. The vapor helps to form a conductor 
for the current and becomes incandescent. This incandescent vapor 
is not the chief source of light, for solids are better radiators than 
gases, and the carbon tips are much hotter than the vapor. The 
temperature is so high that the positive carbon actually boils, and 
this glowing portion is the chief source of light. 

The vaporization goes on most intensely in the center of the posi- 
tive carbon, lessening as the distance is increased from the center, 
and this burns a hollow-shaped cavity in the positive carbon form- 
ing what is known as the crater. This crater is the source of most 
of the heat and light, very little coming from the arc, and scarcely 
any from the negative carbon. 

As the carbon vapor is projected across to the negative carbon, 
part of it condenses and builds up this carbon to a conical point, 
though the carbon as a whole burns away. 

The positive carbon is supposed to be at a temperature between 
5000° C. and 6000° C, while the negative carbon is probably be- 
tween 2000° C. and 3000° C. On account of this difference in 
temperature, the positive carbon wastes away faster than the nega- 



Arc Lights 597 

tive one. and, as it has been said, part of the vapor from the 
positive carbon condenses on the negative one. 

The above considerations are only true for arc lights produced 
by continuous currents, but if the arc is produced by alternating 
currents, the electrodes are acted upon alike in every particular, for 
one is positive at one instant and negative at the next; and they 
-will be consumed at equal rates and will assume the same shape in 
their tips. 

In continuous currents, the rate of consumption of the positive 
carbon is about twice as great as that of the negative one, and the 
rate of consumption depends on whether the arc is enclosed or not. 

Back E. M. F. — In addition to the ohmic resistance of the arc 
it has the peculiarity of exerting a back or counter E. M. F. This 
back E. M. F. opposes the applied E. M. F. of the circuit producing 
the arc and seems to range between 35 and 40 volts, many experi- 
ments seeming to show that 39 volts is about the average value of 
this E. M. F. This shows that to operate successfully an arc light, 
the impressed voltage must be of a value sufficiently high to over- 
come the back E. M. F. as well as to overcome the ohmic resist- 
ance of the arc. This latter varies almost directly with the dis- 
tance between the carbons. In the arc, it should be remembered 
that the voltage varies directly as the length of arc and the current 
inversely. This means that the farther the carbons are apart, the 
greater the difference of potential between them, and the less the 
current that flows between them, and to this extent Ohm's law is 
not applicable. 

The explanation of the back E. M. F. is given by Professor S. P. 
Thompson as follows : In the transformation of the carbon from 
the solid to the gaseous state, a certain amount of latent heat is 
absorbed by the vapor without raising its temperature. As this 
vapor condenses on the negative carbon, this latent heat is released 
and in doing this it develops, in a reverse sense, the electrical energy 
which produced the original transformation of the vapor. 

Resistance of the Arc. — The true resistance of the arc depends 
on the ohmic resistance of the space separating the carbons, and 
the resistance of the back E. M. F. which is sometimes called the 
apparent resistance. The ohmic resistance depends on the distance 



598 Naval Electricians' Text Book 

separating the carbons and may vary between y 1 ^ and 10 ohms, 
while the apparent resistance is a fixed quantity. In an open-type 
arc taking 10 amperes with a length of arc giving -J ohm resist- 
ance, the E. M. F. necessary to overcome this resistance would be 
5 volts, which, added to the 39 volts of the apparent resistance, 
would make 44 volts necessary to operate such an arc. Ordinary 
open arc lights take from 45 to 55 volts and enclosed arcs from 60 
to 160 volts. 

An arc lamp has one length of arc with which it will act best, 
and a lengthening of it will produce flaring of the flame, and the 
flame will leave the tips and burn around the edges, while a short- 
ening will produce violent hissing and sputtering. With the proper 
length of arc the flame will burn quietly and smoothly. 

Carbons. — The carbons used for arc lights are generally made 
from graphite, a powdered form of carbon, deposited on the inside 
of the retorts used in the manufacture of coal gas. It is powdered, 
mixed with a syrup to make the particles adhere firmly and then 
molded in the proper form and baked hard. They are made with 
an inner core of softer carbon, having less resistance than the out- 
side, thereby tending to hold the current near the center of the 
carbon, facilitating the first formation of the crater in the center 
and keeping it there. The finished carbons are given a thin electro- 
plated coating of copper which increases the original conductivity 
of the carbon, besides adding to its duration from 30 to 40 per cent. 

The size of the carbons depends on the current used, one for 50 
amperes, as a search-light, requiring a diameter about -fj- to J-f of 
an inch. On account of the boiling of the positive carbon, it wears 
away about twice as fast as the negative one, this last losing by the 
incandescent particles of carbon being thrown against it, tearing 
and wearing it away. The negative carbon is smaller in diameter 
than the positive as it does not lose as much as the positive. The 
lengths depend on the time they are required to burn, one 12 inches 
long will burn from 7 to 12 hours in an open arc, but in a closed 
arc, a* pair of ordinary carbons will sometimes last 150 hours. 

Regulation of the Arc. — While the arc lasts, the carbons are 
quickly consumed, and the air gap widens until a point is reached 
when the resistance is so great that the current will no longer main- 



Arc Lights 599 

tain the arc and the flame or arc is extinguished. To relight, the 
carbons must be touched again and at the instant the current flows, 
must be separated the proper distance. 

The lamp of an arc light must then automatically (1) cause the 
regular and gradual approach of the carbons towards one another, 
or one toward the other; (2) produce the initial spark by bringing 
the carbons in contact and separating them the proper distance at 
the instant current is established ; (3) hold the carbons at a certain 
distance, called the length of arc, previously determined for the cur- 
rent used and the intensity of light required. 

The lamp of a search-light must satisfy the above three condi- 
tions and in addition must (4) provide means by which the arc is 
kept continually in the focus of the mirror, as the positive carbon 
wears away faster than the negative one. All four of the. above 
conditions are satisfied in the construction of the search-light lamp, 
partly by mechanical and partly by electromechanical means. 

Principles of Regulation of Search-Light Arcs. 

Arc lights used as search-lights on board ship require on an aver- 
age of 45 volts between the carbons to produce and maintain a 
steady arc, about 39 volts being absorbed in doing the work of vapor- 
izing the carbon. As search-lights are worked in parallel with 
incandescent lamps, requiring a higher voltage, a dead resistance 
must be inserted in each search-light circuit to cut the voltage down 
to the required difference of potential between the carbons. As the 
light given out depends on the number of watts absorbed, both the 
voltage and amperage may be varied, the former, however, within 
very narrow limits. 

We have thus two electrical factors to vary, volts and amperes, 
the varying factors being the length of arc and the resistance in the 
circuit. These four are intimately connected, a variation in either 
the length of arc or of the resistance producing changes either in 
the difference of potential or current or in both. 

For a certain maximum length of arc, the least difference of 
potential between the carbons is fixed, and with this length of arc 
the current may be varied by changing the dead resistance. If 
from any cause the length of arc becomes smaller the difference of 



600 Naval Electricians' Text Book 

potential decreases, but the current increases without any change in 
. the dead resistance. So, if a certain difference of potential is de- 
cided on the current may be carried by a change in the dead 
resistance. 

If a certain current is decided on, it can be obtained by changing 
the length of arc, or if that is fixed, by changing the resistance, or 
both may be changed. 

If both the differences of potential and current are fixed, the 
former can be regulated by giving the maximum length of arc, and 
then the current can be obtained by varying the dead resistance. 
This last condition is the one generally adopted in actual practice, 
the difference of potential or maximum length of arc, being ad- 
justed by the tension of a spring acting against the mechanism 
which, feeds the carbons together, and this then being a fixed quan- 
tity, the desired current is obtained by one certain fixed resistance. 
This, presupposes that the lamp is perfectly automatic, that is, it 
keeps the arc constantly at the same length, and if such were the 
case, it would require no further attention. 

However, no lamp is perfectly automatic, and any consequent 
change in the arc must be corrected, while the lamp is working, 
by varying the resistance. 

In most lamps, there is no provision made for feeding the car- 
bons apart if by any chance they get too close, and while they are 
naturally wasting away, the current must be controlled by the resist- 
ance. If the carbons get too far apart, the mechanism then acts to 
feed them together. 

Action of the Dead Resistance. 

Fig. 278 shows the action of the dead resistance in the circuit 
in causing the necessary drop in potential, B being the resistance 
introduced in series with the main current and B' representing the 
resistance of the arc. 

If the carbons are far apart, so that B f is practically infinite, a 
voltmeter connected as shown at V would indicate the full voltage 
of the circuit and one connected to the terminals of the resistance 
B would not indicate, the circuit through it not being complete. 

If the arc is once struck so that the resistance of the main circuit 



Arc Lights 601 

is very much lowered, and a large current flows through R! , V will 
then indicate the difference of potential at the carbons, or the fall 
of potential through R' , and V will indicate the fall of potential 
through R. Knowing the current desired and the drop through 
R' necessary, R may be calculated to give the proper drop through 
it. When the current is flowing the sum of the two readings of 
V and V will be the same as that indicated on V when no current 
was flowing through R'. 

The figure shows a typical search-light circuit, ammeter A being 
inserted in the circuit, V connected as shown, V being omitted, as 
the reading obtained by that can be obtained on the switchboard 
voltmeter, as it is in fact the full voltage of the generators. 



© 



a 



1 



Fig. 278. — Action of Dead Resistance. 

The resistance R should always be of such a value as to cause 
steady working and of sufficient reserve to prevent a short circuit in 
the mains. It should be sufficiently large to withstand heavy cur T 
rents without undue heating, with provision for ventilation. 

Calculation of R. — Suppose a search-light was to be worked at 
50 volts, and of sufficient size to carry 50 amperes, then the resist- 
ance of the arc would be, R = — T or R = — . — 1 ohm. If the full 

voltage was 80, the fall through the resistance R! must be 80 — 50 
= 30 volts. The current through R! being 50 amperes, by Ohm's 

law E = CR or R = ^ , R — |? = \ ohms. 

3 E 

The total resistance then in circuit is 1 — j— -— - ohms or C = ^ 

o K 

where E and R represents total E. M. F. and total R, 

80 
or C = o =50 amperes. 

i+4 



602 



Naval Electricians' Text Book 



This is also arrived at as follows : 

CD is the fall through the arc and DE is the resistance of arc, 
AB is total fall and x is the resistance to be inserted, then by similar 
triangles (Fig. 279), 

i5 'Uflf 80- . . _3 

5 ' 



CD 



+ x 80 
^ Or 50 



l + x ° r x = 




D 

Fig. 279. 



Horizontal Lamp. 

Having now shown what a good automatic lamp should be capable 
of doing as explained under regulation of the ( arc, a description of 
one horizontal lamp now used in the service will be given. 

Fig. 280 is intended to show the general working mechanism of 
the lamp and the action of the current is making it automatic. 
Current is brought to the lamp from slide contacts in the projector, 
these contacts receiving current from the mains through a switch in 
the pedestal of the projector. When the lamp is placed in position 
in the barrel of the projector, the terminals of the lamp press 
against the slide contacts, making sliding connection, to enable the 
lamp to be moved in and out from the mirror for the purpose of 
focusing. The lamp terminals are shown at a, being one on each 
side, the further one, positive, not showing in the figure. From the 
positive terminal, the current flows around an electromagnet b in 
series with the main current ; the end of the magnetizing coil being 
secured at c, on the iron piece d, which in turn is secured to the 
core of the electromagnet. The iron piece d is in contact with the 
metal framework of the lamp, the sides of the frame being shown 
removed. Any part or point of the frame may be considered as the 
positive terminal of the arc, as it is in direct metallic connection 
with the main current. 



Arc Lights 



603 



From the piece d in contact with the frame, current finds its way 
through the end pieces of the framework, through the screw spindle 
e, through the two upright supports of the positive carbon f, 
through the positive to the negative carbon, down the two uprights 
g, through the connecting piece h to j and down the latter to the 
negative terminal of the lamp. The uprights g are insulated from 
the rest of the framework, this allowing all the framework to be of 




Fig. 280. — Horizontal Lamp. 



the same potential. Current also finds its way from the side at % to 
the positive uprights, the uprights / being provided with flanges 
sliding in slots in the side of the frame. 

For the automatic working of the lamp, there is a shunt circuit 
taken from the main current, this shunt circuit . controlling the 
automatic mechanism. The positive terminal of this shunt circuit 
may be considered as any part of the framework, such as the point 
where the armature n of the electromagnet 2 is pivoted to the 
frame. The shunt current from here flows through the armature 



604: Naval Electricians' Text Book 

n, through the flat copper spring H, which acts as a contact breaker, 
through the contact point on the bracket Q, through the bracket G 
which is insulated from the frame, through and around the electro- 
magnet 2, to the automatic switch 3 and to a point on j, acting as 
the negative terminal. 

The two uprights / are connected at the bottom by a cross-piece 
to which is secured a lug with a thread cut in it and through which 
screws the spindle e. A rotary motion given to e causes the up- 
rights carrying the positive carbon to move along the spindle. 
Motion is given to the uprights g carrying the negative carbon in 
a similar manner by the rotation of the spindle B. This spindle 
also has a lengthwise motion through its bearings in the ends of the 
frame, allowing the uprights to be moved a short distance without 
a rotary motion of B. This provision is made in order to strike 
the arc, and to do this one carbon must move independently of the 
other, thus necessitating a flexible connection. In striking the arc, 
the two uprights g move and they are connected to the upright j, 
a rigid solid conductor, by a conductor of flexible copper ribbon, of 
a shape shown on the right at h, so when g is moved to the right or 
left, the copper ribbon bends back or unrolls on itself. 

The spindles B and e are connected to each other through the 
gear wheels C and E, and if the spindle e is turned the carbons are 
either brought closer together or further apart, the threads being 
right-handed and of equal pitch. To make provision for the posi- 
tive carbon wasting away faster than the negative one and in order 
to keep the arc always in the same place, the gear wheel C is twice 
the size of E, so a motion given to E will only cause half the motion 
in C, or in other words, any rotary motion given to the spindle e 
will cause the positive carbon to either approach or recede from the 
negative one at a rate twice as great as the negative carbon moves. 

The uprights holding the carbons have clamp screws to hold them, 
and the positive one is fitted with tangent screws, by which the end 
of the positive carbon may be slightly raised or lowered, or turned 
to the right or the left so as to accurately center the arc, and make 
the carbons burn evenly. 

The movement of the spindle B in striking the arc is controlled 
by the electromagnet &, through the armature J, sleeve spindle A 



Arc Lights 605 

and rod K. J is the armature of the series magnet ; pivoted as 
shown, and when attracted towards d, communicates its motion 
through a connecting piece with an end clutch to A which slides 
on a rod, earning K which has a forked arm, engaging the clutch 
on B. When J moves to the right the negative carbon moves the 
same way, the positive one remaining stationary. The amount of 
motion of A to the left is determined by a screw stop-pin through 
the left-hand end piece and to the right by J bringing up against 
the armature d, so the initial separation of the carbons is limited. 

n is the armature of the shunt magnet 2, and when this magnet 
is energized, the armature is attracted, pulling the copper spring- 
contact away from the contact pin, breaking the circuit. The piece 
o pivoted to p is rigidly connected to n, and when n is attracted 
to the magnet, p is pushed up, turning an arm, not shown, carrying 
a pawl F which engages the teeth on D connected to the spindle e. 
When the circuit is broken, n is pulled back in place by the spiral 
spring Tc, hooked to a small screw spindle I, and in doing so, p is 
pulled down, the pawl F revolving the wheel D, which sets in motion 
the spindles e and B, feeding the carbons together. As soon as the 
contact spring H comes in contact with the point, the circuit is 
re-established and the same motions repeated. This make and 
break gives an alternating movement to the feeding pawl as long as 
current flows through the shunt magnet. There is a stop on the 
left not shown which regulates how many teeth the pawl F engages, 
so the feeding may be fast or slow. 

The tension of the spring ~k regulates the difference of potential 
at which the carbons will feed, for the greater the tension, the 
stronger must be the current; or, in other words, the higher the 
voltage necessary to attract the armature n. The tension of the 
spring lc is regulated by two stop nuts m, m. 

Suppose the tension on the spring k has been regulated to give 
the difference of potential at which it is required the carbons will 
feed and the carbons are just touching. The main switch at the 
base of the projector is turned, and immediately the whole current 
flows through the series magnet, the circuit being completed through 
the carbons. At this instant, the series magnet b is energized and 
the armature J attracted, and as has been explained the negative 



606 Naval Electpjcians' Text Book 

carbon is drawn away from the positive, striking the arc. The 
resistance of the arc at this time is such that all the current flows 
through the carbons, there not being enough difference of potential 
between the carbons to cause enough current to flow through the 
shunt magnet to overcome the tension of the spring Tc. The car- 
bons gradually burn away, and as they do, the resistance of the arc 
increases, the difference of potential increases to the amount for 
which the spring k was set and current flows through the shunt 
magnet. This starts the feeding mechanism as explained and the 
carbons are fed together again, the difference of potential gradually 
falling until the spring overcomes the shunt current and the feed- 
ing stops. This arrangement constitutes the automatic working 
of the lamp. If by any chance the carbons get too close, there is 
no provision made for feeding them apart and they must burn away. 

If it is required to work the lamp by hand, the automatic switch 
3 is turned by a wrench on the right-hand end, and this simply 
breaks the shunt circuit, when the carbons can be fed by a wrench on 
the end of the spindle e. 

In order that the arc may be accurately put in the focus of the 
mirror, there is a screw spindle, projecting through the projector 
which screws into a screw thread cut in the face of the lamp 
frame, and turning this moves the lamp towards or from the mirror. 

In horizontal lamps, there is a tendency for the flame to ascend, 
due to the heated air, and to prevent this, and to center the arc 
and make it burn evenly there is a ring of magnetic material sur- 
rounding the arc. This creates a uniform magnetic field around 
the arc which centers it and makes it burn evenly. 

The Balancer. 

The introduction of a dead resistance in the leads of a search- 
light arc to reduce the generator voltage to that required to sustain 
the arc results in the expenditure of energy that does not appear 
as light. This loss is not so great when the arcs take small current 
and the search-lights are few in number, but as both the size and 
number increase the waste energy becomes a matter of great 
importance. 

In the example given, the energy consumed is 80 X 50 = 4000 



Arc Lights 



eor 



watts, of which the arc only consumes 50 X 50 = 2500 watts, a 
waste of 37.5 per cent, and numerically 2 horsepower. This loss 
takes place in the dead resistance and is dissipated in the form of 
heat, the C 2 E loss being 50 X 50 X f = 1500 watts. 

To reduce this loss, the machine known as the balancer has been 
devised. This is similar in appearance to a motor generator, with 
the field of the motor in series with the armature while the genera- 
tor field is differential wound. Its action will be understood by 
reference to Fig. 2 SI, which shows the method of connection to the 
leads. 




Fig. 2S1. — Elementary Connections of the Balancer. 



The arc leads are marked -f- and — (Fig. 281), with the motor 
31 connected in the line, and S is its series field. D is the generator 
connected directly across the line with its shunt field s, FE, field 
rheostat, and SR a starting rheostat. S" is the series field of D 
wound differentially with respect to s. S' is the series winding and 
s' the shunt winding of the lamp-regulating mechanism. 

When the carbons are separated and the main switch closed, cur- 
rent flows as indicated by the arrows. Under this condition, D acts 
as a motor under the action of the constant field due to s and 
drives M. The current through 31 is small, as the carbons are 
separated, and the resistance of s' is high. From the fact that the 
current is small, the field of M through .5' is but feebly energized, 
consequently the counter E. M. F. of M is low. and the fall of 
potential through 31 is also low, being equal to c a r a of 31. The 



608 Naval Electricians' Text Book 

terminals of the lamp shunt s' receive practically the full voltage 
of the line and the shunt current acts to feed the carbons together. 

As soon as the carbons touch and current flows through them, 
the entire condition is changed. The field of M, S, is now fully 
energized and M now acts as the prime mover, driving the armature 
of D. This current flowing through 8" reduces the field of B, as 
the fields are oppositely wound, and reduces the counter E. M. F. 
D acts as a generator and the current through it is reversed. The 
counter E. M. F. of M increases as the field is strengthened, and 
the excess of line voltage over that required for the maintenance of 
the arc is represented by the counter E. M. F. developed. The 
current through M depends on the difference of potential at the 
carbons, on the counter E. M. F. and on the armature resistance, 
and it may be lower than that required to actuate the arc, in which 
case the deficiency is made up by that generated by D. This repre- 
sents the saving effected by this device as the current is not drawn 
from the main generator. 

As the carbons burn apart and the resistance increases, the field 
current of M decreases and the armature speeds up. This decrease 
of current decreases the series effect of D, and both causes, the in- 
crease of speed and field, results in an increase of the difference of 
potential at the lamp shunt terminals and the carbons are fed 
together. 

If the carbons get too close together the increased current causes 
M to slow down, and also decreases the field of D which causes it 
to lower the voltage at the carbon terminals. 

Search-Light Projectors. 

The projector carrying the lamp consists of a fixed pedestal sur- 
mounted by a turntable carrying the projector proper. The pedestal 
is arranged so it can be securely bolted to the deck or platform and 
fitted to contain the electrical connections. 

The turntable is so designed that it can be revolved in a horizontal 
flame freely and indefinitely in either direction or clamped rigid 
if desired. 

The drum is trunnioned on two arms bolted to the turntable and 
has free movement in a vertical plane of 70° above and 30° below 



Arc Lights 609 

the horizontal. The drum can be rotated on its trunnions by hand 
or clamped rigidly in any position, and while clamped may be given 
a slow movement in altitude by turning a small handle in the axis 
of the pedestal. The drum is fitted with peep sights for observing 
the arc in two planes, in the side by a colored piece of glass and in 
the top by reflecting prisms. The drum is designed to contain a 
parabolic mirror. 

The mirror is of the best quality of glass and should be free 
from all flaws and holes, with its surface ground to exact dimen- 
sions. The back is silvered in such a way as to be unaffected by 
heat. The glass is mounted in a separate metal frame lined with 
a non-conducting material to allow for expansion due to heat, and 
to prevent injury from concussion. 

The front of the drum is provided with a glass door composed 
of strips of clear plate glass. 

The lamps produce the best results when taking current as 
follows : 

13-inch 18 to 20 amperes. 

18-inch 30 " 35 

24-inch 40 " 50 

30-inch 70 " 80 

60-inch 150 " 200 

The 18-inch projector is supposed to project a beam of light of 
such intensity as to render plainly discernible, on a clear dark 
night, a light-colored object 10 X 20 feet in size, at a distance of 
not less than 4000 yards, the 24-inch projector at a distance of not 
less than 5000 yards and the 30-inch projector at a distance of not 
less than 6000 yards. 

For the care and management of search-lights see chapter XXXV. 

Enclosed Arc Lamps. 

Enclosed arc lamps are now being used on shipboard to some 
extent, especially in engine-rooms, where a large area requires gen- 
eral illumination. These lamps differ from ordinary arc lights in 
that the arc is surrounded by a small glass globe which fits the 
carbons so closely that the air inside the globe can only slowly 
change. One effect of this is to reduce the rate of combustion of 



610 



Xaval Electricians 7 Text Book 



the carbons which also lessens the work of the feeding mechanism. 

The enclosed air becomes a source of light, so that the whole globe 

seems to glow and increases the apparent amount of light. 

Enclosed arc lights require a higher voltage than open arcs, 60 

volts being about the minimum, and take from 2 to 10 amperes. 
Lamps are furnished to operate on voltage of 80, 110 or 125 

volts with a current not exceeding 4.5 amperes. The arc is enclosed 

by an inner opal globe, which is 
surrounded by a clear globe pro- 
tected by a composition guard. 
The guard and outer globe are 
removed together and so held by 
supporting chains that the inner 
globe may be removed to renew 
the carbons. 

Carbons are -J inch in diameter 
and have a life of 120 hours with- 
out trimming. 

Each lamp contains the proper 
resistance for reducing the line 
voltage to that required for the 
best regulation of the arc, an 
average of about 85 volts. 

A commercial form of lamp 
that meets the required specifica- 
tions is made by the General Elec- 
tric Company and is shown dia- 
grammatically in Fig. 282. L t 
and L 2 are the line leads, and are 
wired in multiple from the light- 
ing mains. L x is connected to the 
positive terminal of the lamp P, 
through the switch 8, on top of 
the lamp. From the positive termi- 
nal, the circuit leads to the edge- 
Fig. 282.— Form 12 Arc Lamp, wise wound rheostat R, through 
General Electric Company. the sliding contact B, which can 




Arc Lights 611 

be moved up or down along the rheostat. This throws more or less of 
the resistance of E into circuit and acts as the dead resistance pre- 
viously described. From the rheostat the circuit leads to the 
electromagnets C, C, and thence to the terminal A, which is a part 
of the support holding the upper, positive, carbon of the lamp. 
Current flows from the positive carbon to the lower, negative, 
carbon, then to the curved conductor D, vertical conductor E and 
curved conductor F, up through the center of the rheostat to the 
negative terminal N of the lamp and thence to the line lead L 2 . 

The positive carbon is held by a clutch C through a bell crank 
arm and acts to grip the carbon and raise it when the support is 
raised, but on lowering when the clutch comes against the top of the 
inner globe support, the clutch opens and allows the carbon to fall 
until it brings up against the negative carbon, so at all times the 
lamp is ready for operation. 

Before current is switched on the carbons touch, but as soon as 
the electromagnets are energized, the plunger L is sucked into the 
core of the solenoid, and at the same time the clutch grips the posi- 
tive carbon, raising it, and thus strikes the arc. As the carbons 
burn away and the length of arc increases, the resistance increases, 
consequently the current through the arc lessens and the plunger is 
not held so strongly in the magnets and it drops, until the increased 
current is sufficient to hold it at the proper distance for the voltage 
across the arc. 

The working mechanism of the lamp is protected from dust and 
dirt by a bronze sheet-copper casing, and there should be no occa- 
sion to remove this as the rheostat is properly adjusted and should 
not be changed. 

Candle-Power of Arc Lights. 

The candle-power of arc lights is rather a deceptive means of 
determining how much light an arc is producing. For instance, a 
so-called 2000-candle-power arc light does not give more than 1400 
candle-power in the direction of greatest intensity. The same con- 
siderations hold for arc lights as for incandescent lights regarding 
their mean spherical candle-power ; that is, it is the average candle- 
power on the surface of a sphere with the light at the center. 



612 Naval Electricians' Text Book 

However, there is a great difference between the horizontal candle- 
power and the maximum candle-power, the latter being found, in 
vertical arcs with the -f- carbon uppermost on a line making an 
angle of 45° with the horizontal. This is due, of course, to the 
reflection from the crater on the positive carbon, this acting as a 
reflector and throwing the light down, and besides the incandes- 
cence of the positive carbon being the principal source of light. 

An empirical rule for finding the mean spherical candle-power 
is to add one-half the mean horizontal candle-power and one-quarter 
of the maximum candle-power. From the direction of the maxi- 
mum ray, it is very evident that for a search-light to give out the 
most light, the carbons should be so placed that the rays of greatest 
intensity shall be the ones that should be reflected from the mirror. 
In other words, the carbons should be horizontal, with the positive 
carbon farthest from and pointed towards the mirror, and this is 
the case with all present designs of search-lights. 

The practical method of determining the candle-power is to find 
the power in watts absorbed to produce it. The mean' spherical 
candle-power can be determined by using the arc in connection with 
the photometer, finding both the horizontal and maximum candle- 
power; and at the same time by properly connecting a voltmeter 
and ammeter, the number of watts absorbed can be found. When 
the arc is used as a search-light, and the product of the volts and 
amperes show a value equal to that found when the candle-power 
was being tested then the arc is producing its rated candle-power. 
Different shaped carbons or different adjustments may vary the in- 
tensity or direction of the maximum ray, but with the same number 
of watts, the mean candle-power remains practically the same. 

The maximum candle-power can be determined by connecting a 
voltmeter and ammeter in circuit, and varying these quantities until 
their product is a maximum. The range of voltage is practically 
limited to a few volts, the greatest current consistent with steadiness 
of arc, proper length of arc and the carrying capacity of the carbons 
may be found. When a light is being used under the conditions 
determined for maximum candle-power, or the product of the two 
variables is the same, then it may be certain that the arc is giving 
its maximum mean spherical candle-power. 



Arc Lights 613 

Flaming Arc Lights. 

In the ordinary carbon arc light, most of the light is produced 
bv the incandescence of the carbon terminals, and improvements 
have been made in making the arc itself luminous. The addition 
of materials such as calcium and strontium to the carbons results in 
the production of very highly luminous and efficient arcs. The 
carbons produce a vapor path by which the light-producing ma- 
terials are conveyed from one terminal to the other. From the 
appearance of these arcs, they are called " flaming arc " lamps. 
Their efficiency is about ten times as great as that of the carbon 
arc. On account of the fumes given off by these arcs they can only 
be used for outdoor lighting or in places where there is good 
ventilation. 

Mercury Vapor Lamps. 

This lamp consists of a glass tube, which may be of different 
lengths, exhausted of air and connected to a reservoir of mercury. 
This metallic mercury forms one electrode while the other is at the 
end of the tube farthest from the reservoir. The arc is started by 
tilting the tube, making metallic contact from one electrode to the 
other. The heat produced by the current maintains a supply of 
vapor which forms a conducting path for the current. This con- 
denses along the sides of the tube and runs down again to the 
reservoir. This lamp gives off a greenish light of very high in- 
tensity. The spectrum shows an absence of all red rays, and the 
light cannot be used when colors are to be compared, but makes a 
very satisfactory light for general illumination or reading. To a 
certain extent the candle-power of the lamp is controlled by the 
diameter of the tube. 



CHAPTER XXVI. 

WIRES. 

The size of a conductor necessary to carry a given current is 
determined by its area of cross-section, and this may be any of the 
ordinary shapes; square, rectangular or circular, the latter being 
the most common. If the cross-sectional area be circular, as a wire, 
the conducting area may be one large wire, or a collection of wires 
stranded together carrying the current in parallel and whose area is 
collectively equal to the large wire. 

Circular Mil. — Electricians use as a unit of sectional measure an 

area whose value is one circular mil. The mil is a linear measure 

and is equal to .001 of an inch. If a round wire has a diameter of 

one mil, then the area of cross-section of that 

wire is one circular mil. 

The square mil is sometimes used as a unit 
of area, being the area of a square .001 inch 
on a side. The number of circular mils multi- 
plied by .7854 gives the number of square mils ; 
Fig. 283. and the number of square mils multiplied by 

1.273 gives the number of circular mils. This 
is shown in the relation between the area of a circle and the circum- 
scribed square, 1 mil on the side (Fig. 283), 

area of circle = ^ = '^4^ X I 2 = .7854 sq. mils = 1 cir. mil, 

area of square = 1X1 = 1 sq. mil, 

or .7854 X 1 sq. mil = 1 cir. mil, 

1 cir. mil. X 1-273 = 1 sq. mil. 

When the diameter of the wire is .001 inch or one mil, the cir- 
cular area is .001 2 X .7854 = .0000007854 square inch, or one cir- 
cular mil = .0000007854 square inch. 

Suppose it was required to express in circular mils the area of 




Wires 615 

cross-section of a wire 1 inch in diameter. The area of this circle 
would be 

^ = .7854 X I 2 = .7854 sq. inches. 
4 

But 1 cir. mil = .0000007854 sq. inches, 

No. of cir. mils = ^^07854 = 1 ' 000 ' 000 - 
This number is the square of the diameter expressed in mils, as 
one inch equals one thousand mils; hence we have the rule: To 
express the cross-sectional area of wires in circular mils, we multiply 
the diameter of the wire expressed in mils by itself; or, in other 
words, the square of the diameter expressed in mils is equal to the 
area in circular mils. 

To express the cross-sectional area of a rectangular or square- 
shaped conductor in circular mils, it is necessary first to find the 
area in square inches, and reduce that to circular mils. 

1 sq. inch = 1,000 X 1,000 = 1,000,000 sq. mils, 
1 sq. mil = 1.273 cir. mils, 
or 1 sq. inch = 1,273,000 cir. mils. 

So to find the area of a bus bar, for instance, first find its area 
in square inches and multiply by 1,273,000, and the result will 
be circular mils. 

Wire Tables. 

Wires are made in standard sizes, and numbers are given each 
size, this number expressing the area of cross-section in circular 
mils as determined by their diameters. Gauges are made by which 
the diameters of wires are measured, and a reference to a wire table 
made for the gauges used gives the area in circular mils. The 
two principal wire tables and gauges are those of Brown & Sharpe 
in America and the Birmingham in England, called respectively 
the B. & S. gauge and B. W. Gr. gauge. 

In the following table the dimensions are given for single wires, 
though conductors are rarely composed of only one wire, but rather 
made up of stranded wires, such that the carrying capacity of the 
stranded wires in parallel is approximately equal to one large con* 



616 



Naval Electricians' Text Book 



ductor. For instance, suppose a wire of 30,000 circular mils was 
required; a No. 7 B. W. G. would answer the purpose, but for 
pliability and ease in installing, it would usually be made up of 
7 strands of No. 16 B. W. G., giving 7 X 4225 = 29,575 circular 
mils or 19 strands of No. 18 B. & S., giving 19 X 1624 = 30,856 
circular mils. 



WIRE TABLES. 



Gauge. 


Diam. 


Area. 


Gauge. 


Diam. 


Area. 


B. & S. 


B.W.G. 


Inches. 


Sq. in. 


Cir. 

Mils. 


B.& S. 


B.W.G. 


Inches. 


Sq. in. 


Cir. 
Mils. 


0000 




.460 


.1662 


211.600 




8 


.165 


.0214 


27.225 




6666 


.454 


.1618 


206.116 


"*6 




.162 


.0206 


26.250 




000 


.435 


.1419 


180.525 




"*9 


148 


.0172 


21.904 


'666 




.409 


.1318 


167.800 


'"7 




.144 


.0163 


20.736 




"66 


.380 


.1134 


144.400 




' io 


.134 


.0141 


17.956 


"66 




.364 


.1046 


133.100 


"*8 




.128 


.0129 


16.610 




'"6 


.340 


.0908 


115.600 




"i2 


.109 


.0093 


11.881 


'"6 




.324 


.0824 


105.500 


"io 




.102 


.0082 


10.380 




"i 


.300 


.0727 


90.000 




"ii 


.083 


.0054 


6.889 


*"i 




.289 


.0657 


83.690 


"ii 




.09074 


.0065 


8.234 




2 


.284 


.0633 


80.556 


12 




.081 


.0051 


6.530 




3 


.259 


.0527 


67.081 




"ie 


.065 


.0033 


4.225 


"2 




.257 


.0521 


66.370 


""is 




.07196 


.00407 


5.178 




'"4 


.238 


.0445 


56.644 


14 




.0641 


.0032 


4.107 


'"3 




.229 


.0413 


52.630 




"is 


.049 


.0019 


2.401 




'"5 


.220 


.0360 


48.400 


"i.5 




.05707 


.00256 


3.257 


"*; 




.204 


.0328 


41.740 


16 




.051 


.0020 


2.583 




"*6 


.203 


.0324 


41.209 


17 




.04526 


.00161 


2.048 


'"5 




.182 


.0260 


SB. 100 


18 




.040 


.0013 


1,624 




""7 


.180 


.0254 


32.400 


19 




.03589 


.00110 


1.288 



Wires are usually referred to as so many even thousand circular 
mils; thus a No. 16 B. W. G. is 4225 circular mils and a No. 14 
B. & S. is 4107 circular mils, both of which would be spoken of as 
4000 circular mil wire. 

For ship installation when a conducting area greater than that 
of No. 14 B. & S. is required, the conductor is stranded, the com- 
plete wire being composed of an odd number of strands, and the 
size of strands and single conductors are determined by the B. & S. 
gauge. The conductors are stranded in a series of 7, 19, 37, 61, 
91 or 127 wires as required. The total conductor consists of a 
central strand, the remainder laid around it concentrically, each 
layer twisted in the opposite direction from the preceding. 

The following table gives the actual size of wires and the number 
of strands as manufactured for the navy : 



Wires 



617 





Actual 


No. 

wires 


Size of 
wire. 


Diameter inches. 


Diameter in 32ds of an 
inch. 


Approx. 
C.M. 










Over 
all 
insula- 
tion. 


CM. 


in 
strand. 


B. &S. 
G. 


Over 
copper. 


Over 

Para 

rubber. 


Over 

vulc. 

rubber. 


Over 
tape. 








No. 












4,000 


4,107 


1 


14 


.06408 


.0953 


7 


9 


11 


9,000 


9.016 


7 


19 


.10767 


.1389 


10 


12 


14 


11.000 


11.368 


7 


18 


.12090 


.1522 


10 


12 


14 


15.000 


14.336 


7 


17 


.13578 


.1670 


10 


12 


14 


18.000 


18,081 


7 


16 


.15225 


.1837 


11 


13 


15 


20.000 


22,799 


7 


15 


.17121 


.2025 


12 


14 


16 


30.000 


30,856 


19 


18 


.20150 


.2328 


12 


14 


16 


40.000 


38,912 


19 


17 


.22630 


.2576 


13 


15 


17 


60.000 


49,077 


19 


16 


.25410 


.2854 


14 


16 


18 


60.000 


60,088 


37 


18 


.28210 


.3134 


15 


17 


19 


75,000 


75,776 


37 


17 


.31682 


.3481 


16 


18 


20 


100.000 


99,064 


61 


18 


.36270 


.3940 


18 


20 


22 


125.000 


124,928 


61 


37 


.40734 


.4386 


19 


21 


23 


150.000 


157,563 


61 


16 


.45738 


.4885 


20 


22 


24 


200.000 


198.677 


61 


15 


.51363 


.5449 


22 


24 


26 


250.000 


250,527 


61 


14 


. 57672 


.6080 


24 


26 


28 


300.000 


296.387 


91 


15 


.62777 


.6590 


26 


28 


30 


375.000 


373,737 


91 


14 


.70488 


.7361 


29 


31 


33 


400.000 


413.639 


127 


15 


.74191 


.7732 


30 


32 


34 


500.000 


521,589 


127 


14 


.83304 


.8643 


32 


34 


38 


650.000 


657.606 


127 


13 


.93548 


.9667 


35 


37 


42 


800.000 


829.310 


127 


12 


1.05053 


1.0818 


39 


41 


46 


1,000,000 


1,045,718 


127 


11 


1.17962 


1.2109 


43 


45 


50 



Wires Used in Strands. 



1,288 
1,624 
2,048 
2,583 
3.257 
4.107 
5.178 
6,530 
8,234 



.04030 
.04526 
.05082 
.05707 



.07196 
.08081 
.09074 



Insulation of Lighting Wire. 

Lighting wire used for light and power mains is classed as single 
conductor, twin conductor and double conductor. The standard 
dimensions for single conductor is given in the preceding table. All 
conductors are of soft annealed pure copper wire. The conductivity 
of each single wire must be not less than 98 per cent of pure copper 
of the same number of circular mils, and the conductivity of the 
whole standard conductor must be at least 95 per cent of pure 
copper of the same number of circular mils. 

Each wire, whether forming a single conductor or a strand of 
a stranded conductor, is thoroughly and even tinned. This is to 



618 



Naval Electricians' Text Book 



prevent any corrosive action between the sulphur in the vulcanized 
rubber and the copper of the wires. 

All single conductors are insulated as follows : 

1. A layer of pure Para rubber -£% inch thick, rolled on. 

2. A layer of vulcanized rubber. 

3. A layer of cotton tape. 

4. A close braid of No. 20 2 -ply cotton thread braided with three 
ends for all conductors under 60,000 circular mils, and No. 16 
3-ply cotton thread, braided with four ends, for all conductors of 
and above 60,000 circular mils. 

Twin Conductors. — The standard dimensions for these conductors 
are given in the following table : 







a 


6 

GO 


Diameter in 
inches. 




Diameter in 32ds of an 


inch. 






2 

0Q 


oq 














g 




,Q 


i fc 


Over 


Over 


Over 2d 


si 

o 

3 

© 


a 
© 

6 


© 

% 

O 
© 

2 


© 

Pi 

O 
© 

© 


3 

e 

s© 


Id 
^ © 


tape. 


1st braid. 


braid. 


o 

M 
o 

ft 
p. 


83 

s| 


82 


ne con- 
ductor. 

wo con- 
luctors. 


« 6 

8° 

©2 

Er3 


83 


< 


< 


ft 


s 


o 


O 


o 


o^ 


eh^ 


O^ 


EH^ 3 


o^ 


^ 


4,000 


4,107 


1 


No. 

14 


.06408 


.092 


5 


6 


12 


8 


14 


10 


15 


9,000 


9,016 


7 


19 


.10767 


.139 


7 


9 


18 


11 


20 


13 


21 


11,000 


11,368 


7 


18 


.12090 


.156 


8 


10 


20 


12 


22 


14 


23 


15,000 


14,336 


7 


17 


.13578 


.172 


8 


10 


20 


12 


22 


14 


23 


18,000 


18,081 


7 


16 


.15225 


.190 


9 


11 


22 


13 


24 


15 


25 


20.000 


22,799 


7 


15 


.17121 


.209 


10 


12 


24 


14 


26 


16 


27 


30,000 


30,856 


19 


18 


.20150 


.243 


11 


13 


26 


15 


28 


17 


29 


40.000 


38.912 


19 


17 


.22630 


.268 


12 


14 


28 


16 


30 


18 


31 


50,000 


49,077 


19 


16 


.25410 


.298 


13 


15 


30 


17 


32 


19 


33 


60,000 


60,088 


37 


18 


.28210 


.327 


14 


16 


32 


18 


34 


20 


35 



All twin lighting conductors consist of two conductors, each of 
which is insulated as follows : 

1. A layer of pure Para rubber -^ inch in thickness, rolled on. 

2. A layer of vulcanized rubber. 

3. A layer of cotton tape, lapped ■£% inch. 

Two such insulated conductors are laid together, the interstices 
filled with jute and covered with two layers of close braid. Each 
braid is made of No. 20 2-ply cotton thread, braided with three ends. 

Double Conductors. — These are of three varieties, double con- 
ductor, plain; double conductor, silk, and double conductor, diving 
lamp. 



Wires 619 

Double Conductor, Plain. — Each conductor is constructed as 
follows : 

1. A copper conductor consisting of seven Xo. 22 B. & S. G. 
tinned annealed pure copper wires, six of the wires lying around 
the seventh. One conductor is covered with : 

1. A layer of vulcanized rubber. 

2. A close braid of Xo. 60 cotton thread, braided with three 
ends. 

This conductor forms the core, and the wires of the second con- 
ductor are laid around it over the braid concentrically and smoothly. 
Over both conductors are : 

1. A close braid of Xo. 60 cotton thread, braided with three 
ends. 

2. A layer of vulcanized rubber. 

3. A layer of cotton tape -^ inch in thickness. 

4. A close braid of Xo. 30 3-ply linen gilling thread, braided with 
two ends. 

5. A close braid of Xo. 30 3-ply linen gilling thread, braided with 
three ends. 

The fourth and fifth layers of braid are thoroughly saturated 
with a water-excluding compound of such a character as not to 
injure the braid or to render the conductor less pliable. 

Double Conductor, Silk. — Each conductor is constructed as fol- 
lows : 

1. A stranded copper conductor consisting of seven Xo. 25 B. & 
S. G. untinned annealed copper wires, six wires lying concentric- 
ally around the seventh. 

2. A close braid made of Xo. 80 Sea Island cotton thread. 

3. A layer of pure Para rubber to a diameter of -^ inch. 

4. A close braid of Xo. 60 cotton thread. 

5. A close braid of hard twisted olive-green silk. 

6. Two conductors thus constructed are twisted together to form 
the finished conductor. 

Double Conductor, Diving Lamp. — Each conductor is constructed 
as follows : 

1. A copper conductor consisting of seven Xo. 20 B. & S. G. 
tinned annealed copper wires, six of the wires lying around the 
seventh. 



620 Naval Electricians' Text Book 

2. A layer of pure Para rubber rolled on to a thickness of not 
less than -$-% inch. 

3. A layer of vulcanized rubber. 

Two conductors thus constructed are laid up or twisted together 
and filled with jute saturated with an insulating compound. The 
conductors are then covered with : 

1. A layer of vulcanized rubber to a diameter of -JJ- inch. 

2. A close braid of No. 30 3-ply linen gilling thread, braided 
with three ends. 

3. A close braid of No. 30 3-ply linen gilling thread, braided 
with four ends. 

Tests, 

All wires are subjected to a test for continuity and for insulating 
properties; the latter by measurement of insulation resistance and 
by high potential test on the entire length of the cables, either or 
both, as per the following table : 

Insulation resistance. ^^StS? 1 

Lighting wire. 

Up to and including: 

500,000 c. m., single 1000 megohms per knot 4500 

650,000 c. m., single 900 megohms per knot 4500 

800,000 c. m., single 800 megohms per knot 4500 

1,000,000 c. m., single 750 megohms per knot 4500 

All twin wire: 

Between conductors 1000 megohms per knot 3500 

From conductors to ground.. 1000 megohms per knot 3500 

Double conductor. 

Plain: 

Between conductors 1000 megohms per 1000 feet.. 2500 

Each conductor to ground. . .1000 megohms per 1000 feet.. 3500 

Diving: 

Between conductors 1000 megohms per 1000 feet.. 3500 

Each conductor to ground. .. 1000 megohms per 1000 feet.. 3500 

Silk No test 5000 

Tests for insulation resistance are made after immersion of wire 
(not less than three days after manufacture, the three days to be 



Wires 621 

reckoned back from the end of the immersion period) in fresh 
water at a temperature of 22° C. for a period of twenty-four hours,, 
the test to be made by the direct-deflection method at a potential of 
500 volts after five minutes electrification. 

High-potential tests shall then be made with the wire still im- 
mersed, the source of power supply to be a transformer of not less 
than 5-kilowatt capacity. For double-conductor silk and bell cord 
the high-potential tests will be made with the dry wire freely sus- 
pended in the air. 

Tests are also made to determine the percentage of water absorbed 
by the braids, after samples have been immersed in fresh water at 
22° C. for a period of twenty-four hours. 

The braid and insulation must show no breaking or cracking 
when samples are bent to a radius of seven times the diameter after 
having been exposed for several hours at a time, alternately to a 
temperature of 95° C. and the temperature of the atmosphere over 
a period of three days. 

Specifications for Size. 

Search-Light Circuits. — The feeders of search-lights are of sizes 
given in the following table : 

Size of searchlight. Size of feeder. 

c. m. 

13-inch 18,081 

18-inch 30,856 

24-inch 38,912 

30-inch 60,088 

Lighting Circuits. — The maximum load for any feeder for light- 
ing circuits shall not exceed 75 amperes, this on a basis of .5 ampere 
for 16-candle-power incandescent lamps or ^-horsepower fans and 
1 ampere for 32-candle-power lamps of -J-horsepower fans. 

Several mains may be fed by the same feeder provided the total 
load is not in excess of 75 amperes as specified above. 

The area of cross-section of the feeders and mains on the light- 
ing circuits shall be such that the fall in potential from the gener- 
ator terminals to the most distant outlet shall not be more than 3 
per cent at the normal load of the feeder. 



622 Naval Electricians' Text Book 

Any reduction in the size of a feeder or a main shall be fused 
unless the fuse which protects the larger size wire is small enough 
to hold the normal current in the smaller wire down to 1 ampere 
per 1000 circular mils cross-section of wire; i. e., fuse is to blow 
when current density reaches 500 circular mils per ampere. 

No feeder or main shall have a cross-section that will give a cur- 
rent desnsity greater than 1000 circular mils per ampere at the 
normal load. 

Feeders which interconnect shall have an area of cross-section 
of not less than 1500 circular mils per ampere at the normal load. 

Branches for single lights, in conduit wiring, are made of 4107 
circular mils twin conductor. Leads from distribution boxes to 
single outlets are run with 4107 twin conductor. 

Motor Circuits. — Motors whose normal full-load working cur- 
rents are less than 50 amperes may be grouped on the same feeder, 
but no such feeder must have a load in excess of 100 amperes. 
Each motor whose normal full-load working current exceeds 50 
amperes has a separate feeder. 

Feeders and mains have a cross-section not less than 1000 cir- 
cular mils per ampere for continuous service and not less than 500 
circular mils per ampere for intermittent service. 

Calculation for Size. 

In calculating the size of wires for a certain circuit on board 
ship, two requirements must be met : first, the wires must be large 
enough to carry their loads without undue heating, and second, 
they must be large enough so that the fall of potential or drop due 
to the resistance of the conductors themselves shall not exceed a 
certain amount. 

The first requirement is met by the standard specifications which 
state that the safe-carrying load shall be at the rate of 1000 amperes 
per square inch of conductor, and experiment shows that this pro- 
portion is entirely safe, the factor of safety being sufficient. The 
second requirement is that the total drop from the generator to the 
farthest lamp shall be not more than 3 per cent of the total differ- 
ence of potential at the generator, this drop being due to the 
resistance of the conductors. 



Wires 623 

The calculations can best be illustrated by an example showing 
how to find the sizes for feeder, mains and branches in a typical 
feeder circuit to meet the two requirements for heating and drop. 
To take a simple case, suppose a main runs along the gun-deck of 
a vessel, lights being taken from it along its length, and that the 
main is supplied by a feeder from the switchboard at a point such 
that the total current is equally divided, or nearly so, on each side 
of the feeding center. This is represented by the figure. 



wmMmmte 


r<X>WW 


J 
j 

* t af ' 





Fig. 284. 

Fig. 284 represents a main of total double length of 200 feet fed 
by a feeder of 100 feet double-carrying length. There are twenty- 
four lamps represented, sixteen 16-candle-power and eight 32- 
candle-power. For calculation of wire sizes an efficiency of 4 watts 
per candle-power can be assumed, which on an 80-volt circuit would 
mean a current of .8 ampere per lamp, for 

CE = Xo. of watts = 4 X 16 = 64 watts per lamp, 

or C per lamp = _ = .8 ampere. 

Each 32-candle-power lamp would take 1.6 amperes. The total 
load then due to the 16-candle-power lamp is 16 X .8 = 12.8 am- 
peres, and that due to the 32-candle-power lamp is 16 X .8 = 12.8 
amperes. The feeder must supply 25.6 amperes, and the feeding- 
center at such a point that the load on each side of the feeder is 
equal, viz. : 12.8 amperes, which has been assumed 50 feet from 
one end. 

When the wire list is being prepared it is usual to mark the loca- 
tion and character of all lights on the blue prints of the ship, and 
draw the mains, by which means the exact total load the mains must 
carry is determined, and also the length of the mains. The proper 
feeding center is then determined on and the length of the feeder 
to the switchboard measured. 



624 Naval Electricians' Text Book 

The resistance of a foot of copper wire at 75° F., and 1 mil in 
diameter, or 1 mil-foot, is 10.79 ohms, and since resistance varies 
directly as the length and inversely as the cross-sectional area, the 
general formula for resistance would be 

p 10.79 X L , . 

R = j 2 (a) 

where 

L = length in feet, 

d = diameter in mils, 
or d 2 = area in circular mils. 

From Ohm's law C = ' -L. . (b) 

Where e is the fall of potential between two points whose resist- 
ance is R and through which a current C is flowing. If R is the 
resistance of the conductor, then e is the drop due to this resistance, 
which is the value sought. 

Substituting the value of R in (b) in (a) we have the value 

2 = 10.79 X£XC 

e 

and thus knowing the three quantities L, C and e, the proper size 
wire can be calculated. 

It is, however, usual to see if the size for heating is sufficiently 
large to meet the requirements for drop, and if it is, there is no 
further calculation necessary, but if not, the size for heating must 
be increased. 

Allowing for heating alone at the rate of 1000 amperes per 
square inch, 1 ampere would require 1000 circular mils and the size 
for heating for the feeder would be 25.6 X 1000 = 25,600 circular 
mils. The drop for this size would be 

200X25.6X10.79 __ ,, 
6 = 25^00 =2.16 volts. 

This shows that though large enough for heating, that size is 
too small for the drop, leaving, as it does, only .24 volt for the drop 
in the mains (3$ of 80 — 2.16 = .24). As a rule half the drop 
should take place in the feeder unless it is much shorter than the 



Wires 625 

mains, and assuming that '° * =1.2 volts is the drop in the 

feeder, then 

dr = - 19 = 46,037 circular mils. 

The nearest manufactured size to this would be y-| B. & S., or 
19 X 2583 == 49,077 circular mils, and again using this value 
200 X 25.6 X 10.79 
6 = 4p77 = L12 V0lts - 

Now taking up the drop in the mains, it is seen that there are 
12.8 amperes carried 150 feet on one side of the feeding center, 
and 12.8 amperes carried 50 feet on the other, and it is evident that 
the longer circuit must be calculated for. 

The whole load of 12.8 amperes is not carried the whole length 
of 150 double, or 300 feet, and the drop is proportional to the resist- 
ance. The lamps are taken off at practically equal distances, so the 
drop can be calculated on any average resistance, or for an average 
distance, or half the whole distance. In other words, the calcu- 
lated drop for the whole distance is twice the actual drop. 

It will be shown that the drop in any of the branches is practi- 
cally nothing, so that the drop in the mains, counting the total 

length is 2.4 = 1.12 +-£or x = 2.56, 

or 

, 2 300 X 12.8 X 10-79 

d = 2^6 = 16 > 184 ' 

Using the nearest manufactured size ■£% B. & S. or 18,081 circular 

mils 

_ 300 X 12.8 X 10.79 _ 

e ~~ 18,081 — • ' 

2.29 
The total drop then is 1.12 -f-~ ' % — 2.26, which is within the 

3 per cent limit, leaving .14 for the drop in the longest branch. 

All branch wire is No. 14 B. & S. or 4107 circular mils, so the 
drop in a branch 50 double feet would be 

50 X -8 X 10-79 . 
e = 4io7 = - 10009 ' 

10509 

or per single foot of mains as installed * = .004. 

lit) 



626 Naval Electricians' Text Book 

The size of wire for this circuit would then be : feeder 49,077 cir- 
cular mils; mains 18,081 circular mils, and branches 4107 circular 
mils. 

The section in the mains 50 feet in length could be made of 
smaller wire, for the drop there with the above-sized wire would 
not be as great, but it is usual to make the mains the same size 
throughout. 

The feeder might be made smaller and the mains larger and still 
be within the limit and the selection would depend upon the quan- 
tity of similar-sized wire used in other circuits, so the different 
sizes will be as few as possible. 

If a feeder supplies more than one set of mains, the drop in the 
sub-feeders must be calculated and added to the other calculations 
for feeders and mains. 

When calculating for loops, it is only necessary to allow for a 
length equal to one-half the length of the loop ; that is, if the loop 
is 200 double feet, each side of the feeder would be 100 double feet 
or 200 single feet, or allowing for an average length, it would be 
100 single feet, or half the total length of the loop. The current 
for each 100 single feet would be half the total current carried by 
the feeder. 

The calculations above are based on a unit of resistance at 75° F. 
and if the temperature increases above that limit, the resistance 
will also increase, causing an increase in the drop, but usually there 
is sufficient margin not to exceed the 3 per cent allowed. 

This calculation for drop shows why lamps that require a lower 
voltage to produce their standard candle-power should be placed far 
from the generator, and those that require higher voltage near the 
generator where the drop is least. 

In calculating the drop in power circuits, it is usual to allow a 
little greater drop, for here drop is not of so much importance, 
5 per cent usually being allowed, and of course all the drop takes 
place in the feeder from the switchboard to the motor panel, making 
the calculation very simple. 

In the following examples, take the resistance of 1 foot of copper 
wire 1 circular mil in diameter to be 10.78 ohms. 



Wires 627 

Problems on Size and Drop in Wires. 

1. A motor receives 100 kilowatts of power at a distance of 10 miles 
from a generator, and takes a current of 20 amperes. The loss in the 
wires is to be 10 per cent of the generator output. Find (1) the voltage 
at the motor, (2) at the generator and (3) the diameter in mils of the 
line wires. Ans. 1. 5000 volts. 

2. 5555.5 volts. 

3. 202.5 mils. 

2. A feeder from a generator whose voltage is 110 volts is 100 feet 
to its feeding center. On one side of the feeding center it supplies a 
motor that takes 30 amperes and is 300 feet away. On the other side, 
it supplies 40 incandescent lamps each taking .5 ampere and grouped 
200 feet away, and beyond these two arc lamps in series. Allowing 
2 per cent drop in the feeder, calculate the size necessary. If the size 
of the wire supplying the lights is 33.332 circular mils, find the voltage 
across each arc lamp. Calculate the size required for the motor mains, 
allowing 5 per cent drop. Ans. 1. 53.900 cir. mils. 

2. 52.28 volts. 

3. 36.000 cir. mils. 

3. What size wire is required to deliver current at 110 volts to a 
motor of 10-H. P. output and 80-per cent efficiency. The E. M. F. of 
the generator is 125 volts and the motor is 500 feet away. 

Ans. 60.943 cir. mils. 



CHAPTEE XXVII. 
WIRING. 

The wiring of al,l ships in the navy presents peculiarities, though 
as a rule it all follows one general system. The distribution of the 
current in ships in commission for lighting and power purposes 
varies according to the size and class of ship, and to a certain extent 
on the time of the installation. The principal modifications in the 
wiring from time to time are intended to effect saving of current 
and at the same time equalize the general " drop " or fall of poten- 
tial around the different circuits. 

In the early days of application of electricity to vessels, the dis- 
tribution of current was a comparatively simple matter, as electric 
lighting was the only consideration, but the demand for current 
for power has increased at such a rate that the general question of 
supply and distribution is one that depends almost wholly on power, 
the lighting current forming only a small percentage of the whole. 

Circuits. 

There are three classes of circuits, each being entirely separate 
and distinct from the others. They are named : 

(1) Search-light circuits. 

(2) Lighting circuits. 

(3) Motor circuits. 

Search-Light Circuits. — Each search-light has a separate feeder 
leading from the dynamo-room, from the search-light panel, 
through a double-pole fused switch, rheostat, ammeter and double- 
pole automatic circuit breaker direct to the terminal in the search- 
light pedestal. Each search-light has its own voltmeter on the 
search-light panel. 

Lighting Circuits. — The lighting system is divided into two divi- 
sions, each division having separate feeders and separate mains: 

(1) Battle service. 

(2) Lighting service. 



WlEING 629 

The battle service includes every light installed below the pro- 
tective deck and every light above the protective deck whose use is 
necessary when the ship is in action. This includes lights for 
operation of guns, at ammunition hoists, at boat cranes, at con- 
trollers, in military tops, on search-light platforms, in conning- 
tower, in turrets, lights in chart houses and pilot house, all signal 
and running lights, binnacle lights, instrument lamps, at blowers 
above protective deck and in passageways and compartments used 
in time of action. 

The lighting service includes all lights not on the battle service, 
lights intended for general illumination in living spaces, passage- 
ways, offices, store-rooms and cabins. 

Motor Circuits. — Motors whose normal full-load working cur- 
rents are less than 50 amperes are grouped on the same feeder, but 
no feeder shall have a load in excess of 100 amperes. 

Each motor whose normal full-load working current exceeds 50 
amperes is fed by a separate feeder with the exception of motors in 
turrets, where motors for the rammer, elevating and ammunition 
hoist are usually on the same feeder. The feeders are unbroken, 
except very long lengths, which are broken in feeder boxes for ease 
in testing. 

General Plan of Wiring for Lighting Circuits. 

The wiring plan in general use is that known as the two-wire 
feeder system. Each circuit is complete in itself through each 
lamp and through the source of supply. This system is in con- 
trast to that using one wire with a common return through the 
body or framework of the ship. 

The feeders are the conductors that lead from the switchboard 
or distribution boards direct to their feeding centers, and they 
supply or feed currents to the mains. If of short lengths, the 
feeders are unbroken from the switchboard to their feeder centers, 
but if of long lengths they are broken in feeder junction boxes, for 
the purpose of testing or ease in installing. ~No lights are taken 
from the feeders. 

The mains are the conductors that run in the vicinity of the 
places to be lighted, and are fed by the feeders. The mains are 



630 Naval Electricians' Text Book 

broken at such places where lights are to be taken off by means of 
junction boxes, and from these junction boxes, conductors are run 
to the lamps. These small conductors from the mains to the lamps 
are called branches. 

A bus feeder is a feeder that runs from a switchboard to a dis- 
tribution board, feeding current to the bus bars on the latter. 

A feeder may supply one or more mains, the branches of the 
feeders then being called sub-feeders. 

Long lengths of mains are undesirable and should be avoided 
•where possible, but it frequently happens these have to be installed 
along the upper decks and in passageways. These long lengths 
suffer considerable drop of potential due to their resistance, and 
the lamps at places far from the feeding centers consequently burn 
dimmer than those nearer the source of supply. (This assumes that 
the lamp gives its rated candle-power at the standard voltage.) 
This is remedied somewhat by using at the far ends of the mains, 
lamps which require lower voltage to produce the standard candle- 
power. 

Loop System. 

In order that all lamps on a circuit shall burn with equal bril- 
liancy at all times, it is necessary that the resistance of the circuit 
from the generator to any lamp shall have a constant value, and be 
equal to the resistance through any other lamp. 
This is partly accomplished in the ordinary tree 
system of wiring, but is much better done in 
the loop system, in which the mains are run in 
the form of closed loops. 

An ordinary loop is shown in Fig. 285, a and 
b representing the feeder and c, c, the mains 
with the lights taken off between thefn. An in- 
spection of this loop will show that the distance 
the current has to flow from the + terminal to 
the — terminal for any one lamp is the same as 
Loop Wiring ^ or an y °t ner lamp, hence the resistance is the 
same and consequently the fall of potential is 
due to the same resistance, and all having the same voltage will 
burn with equal brilliancy. 




Wiring 



631 




This loop has the disadvantage of not furnishing current to all 

the lamps in case of a break in a main. If there was a break at 

d in the positive main, all the lights to the right 

of the fracture would be extinguished. This 

disadvantage does not exist in the next loop, 

though it is not as perfect for equalizing the 

drop. 

In the loop shown in Fig. 286 it is seen that 

in the event of a fracture in either leg of the 

circuit, there will be no break in the continuity 

of the circuit and all lamps will still burn, and 

it would require two breaks in any one leg to 

extinguish a lamp. This is a very ordinary form 

of loop installed on shipboard, usually being 

provided with an interconnecting switch oppo- 
site the junction with feeder. 

Still another modification of the loop system is shown in Fig. 287. 

This is known as the closet 
system, but it does not adapt 
itself very readily for installation 
on board ship, though instances of 
its installation are known. It 
combines the advantages of both 
the other loops, and as a means of 
equalizing potential it is almost 
Fig. 287. — Closet Wiring. perfect. 



Fig. 286. 
Loop Wiring. 




Simple Parallel System. 

Outside of the loop system, the general plan of wiring is that 
of the simple parallel system, as shown in Fig. 2S8. 

The feeders are a and h, feeding the mains c and d from which 
are taken in simple parallel, the lights e, e. Every light is taken 
direct from the mains and that is the general rule, though in some 
cases, there are sub-mains from the principal mains, and lights 
taken from these sub-mains as though from the principal mains. 
To the right of the figure is shown a sub-main g, li, from c, d and 
the lights e, e are taken from this sub-main. In this svstem, the 



632 



Naval Electricians' Text Book 



feeders are brought' to a point where the mains will divide the cur- 
rent equally, as a rule feeding into the centers of the main. To this 
class of feeders is given the name center feeders. If the main is 
practically but a continuation of the feeder, as it is in isolated cases, 
it is called an end feeder. 

This system allows considerable drop along the length of main, 
but the conductors are made sufficiently large to reduce the drop to 
a small amount. It frequently happens that the best all around 
result is obtained by a combination of the two systems. A feeder 




Fig. 288.— Parallel System of Wiring. 



may feed two loops, with sub-mains taken from the loop in which 
the simple parallel system is adopted. 

Loops should be resorted to wherever possible, for though it may 
take more wire in the mains it decreases to some extent the amount 
used in the branches, and the general equalizing of potential and 
current all around the circuit far outweighs any other disad- 
vantages. 

As an instance of the combination of the loop and simple sys- 
tems as installed on board ship, Fig. 289 will show a circuit as 
installed on one of the gunboat class. 

There are feeder boxes at a, ~b, c and d. The main feeder from 



Wiring 



633 



the switchboard comes direct to a, from which run sub-feeders to 
b and c. At d is a sub-main running aft. These loops are on 
different decks, the upper loop running entirely around the half 
deck, through offices, pantries, through and around the cabin. The 
lower loop makes a complete circuit around the wardroom, through 
the state-rooms and wardroom country, the sub-main leading aft 
for lights in store-rooms, and steering engine-room. The sub- 
feeder supplying the lower loop runs up and down, and such a 
feeder is sometimes called a riser. 




Fig. 289. — Parallel Loop System of Wiring. 



This makes a well-balanced combination, in which though there 
is a drop of potential from the generator, there is not a difference 
of J volt measured in any part of the circuit. 

Note. — It might be noted as a point in wiring that in connecting up 
a closed loop care must be taken to connect the proper terminals, other- 
wise instead of making two complete loops of the conductors, it may- 
be connected as one long loop of single conductor, a serious combination 
for the fuses when the circuit is completed. 

"Whenever mains for the lighting circuits are led from feeders, 
it is done through standard junction boxes, having double-pole 
fuses which blow on the basis of 1 ampere per 500 circular mils of 
the main. 



63-1 Naval Electricians' Text Book 






No more than two feeders are ever interconnected and no feeders 
are ever interconnected through their mains. 

All outlets from the mains are fed by branch wires, fused. In 
offices and state-rooms two outlets are usually installed on the same 
branch circuit. Each outlet for magazine lights is run from a 
separate junction box on the mains. 

In the motor circuits when several mains lead from the same 
feeder at any one point, a small distributing panel is sometimes 
used, fitted with double-pole fuses, which blow at double the normal 
current of the motor. 

Marking of Feeders and Mains. 

As a means of identification of the various feeders and mains 
installed in a ship, they are marked at certain intervals with letters 
and numbers according to a plan previously adopted. This is a 
great help during installation and a still greater help after the 
plant is completed. The battleship Connecticut is designed for 
distribution with 82 feeders leading to feeding centers from which 
run 166 sets of mains. As an illustration of the scheme of mark- 
ing, that employed on the Connecticut will be given. The feeders 
are divided into groups according to the following table, and each 
group of feelers is given a letter (capital), this letter being an 
abbreviation of the principal service in the feeder group : 

Lighting feeders, battle service B 

Lighting feeders, lighting service L 

Search-light feeders S 

Ammunition-handling feeders A 

Ventilation feeders V 

Boat-crane feeders C 

Motor-generator feeders M 

Deck-winch feeders W 

Turret-power feeders T 

Miscellaneous-power feeders P 

Nearly every feeder supplies one or more mains and such mains 
are designated by the same number which the feeder carries and a 
small sub-letter. The feeders are numbered consecutively com- 
mencing with 1, thus the first lighting feeder, battle service, is Bl. 
There are 11 battle feeders, so the first lighting feeder, lighting 
service, would be LI 2, etc. 



Wiring 635 

The feeder Bl supplies eight mains, being designated la, lb, lc, 
Id, le, If, lg, lh, the letter designating the kind of service being 
omitted. If there is a sub-main from one of the mains a new series 
of numbers is added to the signification for the mains. Thus the 
sub-main from lb, would be lbl, etc. Eeference to a detailed table 
shows at a glance the nature and location of any main. 

Wiring Installation. 

The general requirements of wiring installation change from 
time to time, but the instructions given under this heading are 
those at present ordered by the Bureau of Equipment in the Stand- 
ard Specifications. 

All wires for feeders, mains and branches are installed in 
enameled steel conduit, except in wing passages, main generator 
and equalizer cables and feeders from switchboard to dynamo-room 
bulkheads, which may be run in iron-strapped insulators, the wire 
in the insulators to be protected from mechanical injury by a metal 
covering of sheet or galvanized iron. 

Thorough water-tightness is observed for all leads into wiring 
appliances and fixtures, through all bulkheads leading into or out 
from a water-tight compartment and through all decks. 

Where conductors on lighting circuits are connected in fixtures 
and wiring appliances, the outer tape and braid on the ends of the 
conductors is to be removed, exposing the vulcanized rubber to 
within J inch of the outside of the gland, and special care must be 
taken not to cut or injure the vulcanized rubber. When the tape 
and braid is removed for connecting up movable fixtures the braid 
ends shall be protected from fraying by whipping the ends of the 
braid and varnishing. 

Water-tighting through bulkheads or decks is secured by the use 
of either of two kinds of stuffing tubes; one form using lamp-wick 
packing, the other red lead. 

All wire run through decks or bulkheads where molding is used 
is led through standard stuffing tubes, and when water-tightness is 
not required, the wires are led through holes bushed with hard 
rubber. 



636 Naval Electricians' Text Book 

Xo feeders or mains are led overhead in places subject to great 
heat, or through or into coal bunkers if it can be avoided. 

Installation of Conduit. — The conduit containing the conductors 
is secured to the metal of the ship by stout straps which in the case 
of bulkheads are secured by machine screws. To attach conduit to 
beams, stifteners and the like, a clamp is used of a design that does 
not require the beam to be drilled. All conduit is to be continuous 
and where passing through water-tight bulkheads, the conduit must 
be made water-tight by standard stuffing tubes. 

Where conduit passes through armor, a hole is first drilled and 
a long nipple inserted, water- tightness secured by jam-nuts on the 
nipple, each side of the armor, set up tight against the armor. 
The conduit is connected to the nipple on each side by a coupling 
or union. 

Lengths of conduit are ordinarily connected by means of unions, 
but in some cases, running threads are used, in which case the 
thread is fitted with an extra half coupling which screws down 
against the full coupling, acting as a lock-nut. The ends of the 
coupling and half coupling are slightly reamed, filled with lamp- 
wick packing and the whole joint treated with red lead. 

Conduits for magazines are made of seamless drawn brass, and 
this is also required for all leads within 12 feet of the standard 
compass. 

Both positive and negative legs of the same circuit are led in the 
same conduit for all conductors of and below 60,088 c. m. All con- 
ductors above this size have a separate conduit for each leg, the 
lengths of conduit for the same circuit being kept as close together 
as possible. 

Installation of Molding. — This is authorized in certain places, 
and when installed consists of three pieces ; the backing strip, mold- 
ing and capping. 

The baching strip, secured first, is secured by brass machine 
screws, no screws coming under junction boxes, switches or re- 
ceptacles and all screws are countersunk. Molding is secured by 
countersunk screws through the center wall to the backing strip. 
Both backing strip and molding is treated with white lead before 






Wiring 637 

being secured together. The capping strip is secured to the mold- 
ing- by round-head screws to the side walls of the molding. 

All wiring accessories shall be separated from the metal of the 
ship by at least J inch of clear solid wood, and they are never 
located over screws securing the backing in place. No double con- 
ductor or twin conductor is used with molding. 

Systems of Distribution. 

It is very evident that no standard method or system of distri- 
bution can be designed that will be suitable for all sizes, classes and 
designs of vessels, and each ship or at least each class will have 
peculiarities which distinguish it from others of different classes. 
It is a different matter distributing 10 electrical horsepower in a 
gunboat of 1000 tons from distributing 1000 electrical horsepower 
in a battleship of 16,000 tons. The switchboard and fittings, such 
as bus bars, switches and fuses, that would distribute and protect 
100 amperes would not serve the same purpose for 7200 amperes, 
the current delivered by the generators of the latest battleships. It 
is not proposed to go into the details of the different methods in 
use in different ships, but an illustration of extreme types will 
serve to show the radical differences, and emphasize the importance 
of learning at once the system of the ship to which one may be 
attached. 

Gunboat Distribution. — As an illustration in this type of vessels, 
one of those at present in commission may serve. This vessel has 
two units, each unit consisting of a generator (engine and dynamo) 
of 4-kilowatt capacity, the generators wound for 80 volts, installed 
in the same dynamo-room. Current from each generator is led to 
a small switchboard, where there are two 3-pole generator switches 
connecting to the bus bars on the back of the board and to the 
equalizing bar for connecting the machines in parallel. From the 
bus bars, the different sections, about ten in all, lead off to different 
parts of the ship. Each circuit is protected on the switchboard by 
two pole fuses. 

On the same switchboard there is one voltmeter with 2-point 
switch for registering the voltage of either dynamo, one ammeter 
for each machine, one field regulator for each machine, and one 



638 Naval Electricians' Text Book 

lamp ground detector with 2-point switch. On a separate panel 
for the one search-light is one voltmeter, one ammeter, one circuit 
breaker and one 2-pole double-throw switch for use with either 
machine. 

Battleship Distribution. — As an illustration of the general dis- 
tribution in this class of vessels, the Louisiana or Connecticut, 
may serve. 

There are eight generators of 100-kilowatt capacity each, the 
generator wound for 125 volts, or a maximum rated capacity of 
6400 amperes. Four of these generators are installed in a dynamo- 
room in the fore part of the vessel and four in another dynamo-room 
in the after part of the vessel. In each dynamo-room there is a 
generator switchboard capable of controlling the four units. Each 
unit has a circuit breaker, voltmeter, ammeter, field regulator and 
switches for connecting to the lighting bus bars, to the power bus 
bars and to the equalizing, bus bar and common negative bus bar. 

For each main generator board there are two feeder panels, one 
for lighting and one for power. The power feeder panel contains 
two 2000-ampere single-throw double-pole switches, to control the 
power current to each of two distribution boards to be described 
later; two 2000-ampere double-pole circuit breakers, one in the line 
to each distribution board, and one 2400-ampere meter to record the 
entire power current from each dynamo-room. The lighting feeder 
panel contains two 500-ampere single-throw double-pole switches, 
to control the lighting current to the distribution boards ; two 500- 
ampere double-pole circuit breakers, one in the line to each distri- 
bution board, and one 800-ampere meter to record the entire light- 
ing current from each dynamo-room. 

In addition to the main generator switchboards there are two 
distribution boards, located one adjacent to each dynamo-room, 
but separated therefrom by water-tight bulkheads. On each dis- 
tribution board there are two sets of bus bars, one for lighting and 
search-lights, and the other for all power circuits. Either set of 
bus bars on either distribution board is capable of being energized 
from the feeder panels of either generator board. 

Each distribution board is composed of three panels, a lighting 
(including search-lights) panel, a power panel and a turret panel. 



Wiring 639 

Each lighting panel contains a 500-ampere double-throw double- 
pole switch for taking total panel load from either dynamo-room; 
a double-pole fused switch for each lighting circuit (eleven from 
each board), a double-pole circuit breaker, a regulator and an 
ammeter for each search-light circuit (three from each board), a 
voltmeter with 3-point switch for the search-light circuits, an 
ammeter to measure the total current on the panel, and a voltmeter 
with 2 -point switch for measuring the voltage of the lighting bus 
feeders from either dynamo-room. 

Each power panel contains one 1500-ampere double-pole double- 
throw switch for taking total panel load from either dynamo-room, 
one double-pole single-throw switch for each power circuit (seven- 
teen from ford board, nineteen from aft), and an ammeter to 
measure the total current on the panel. 

Each turret panel contains one 1500-ampere double-pole double- 
throw switch for taking total panel load from either dynamo-room, 
one double-pole circuit breaker for each turret circuit (twelve on 
each board), an ammeter to measure the total current on the panel 
and a voltmeter with 2-point switch for measuring the voltage of 
the power bus feeders from either dynamo-room. 

Ground detectors, one each of instrument type and lamp type, 
are installed on each distribution board. 

In each turret is located a distribution panel containing a double- 
pole double-throw switch for receiving current from either distri- 
bution board and other devices for controlling the motors in the 
turret in which the panel is placed, including ammunition-hoist 
motors, elevating motors and loading motors. 

In each barbette is located a control panel with instruments for 
controlling the motor generator for each turret, and all appliances 
for the circuits both on the motor and generator side. 

The Protection of Circuits. 

Mention has been made of circuit breakers and fuses in the pre- 
ceding description of current distribution, and their use and action 
will now be considered. 

Fuses. — This is a name given to two entirely different devices, 
both, however, depending upon the heating effect of an electric 



640 Naval Electricians' Text Book 

current, one being used to fire electric explosives and the other to 
protect electric circuits against excessive heat. The last, or safety 
fuse, as it is commonly known, is the one under consideration. 
This is an appliance placed in an electric circuit, designed to carry 
the ordinary amount of current but to melt and break the circuit 
if the current becomes great enough to heat any other part of the 
circuit to a dangerous degree. It is made of such material that its 
resistance is higher than an equal length of the rest of the circuit. 
As the heat developed is C 2 Rt joules, C being the current, R the 
resistance and t the time, it follows that the fuse is always at a 
higher temperature than the rest of the circuit, and on account of 
its low-melting point, any increase above the ordinary current will 
raise the temperature to its melting point and melt it. 

The requirements of a fuse are that it should melt at a com- 
paratively low temperature, that it should melt quietly, that it 
should have hard terminals, and that it should be long enough to 
prevent an arc being maintained after the fuse is melted. There 
should be no reddening or excessive elongation when the current is 
slowly carried up to the fusing point. 

The substances generally used are lead, or an alloy of lead and 
tin, called " half and half "solder. Sometimes bismuth is added 
to lower the temperature of the melting point, and sometimes cop- 
per is used alone where there is no danger from flying sparks. 

Fuses are rated according to the number of amperes taken nor- 
mally by the circuit they are to protect. A 10-ampere fuse is 
intended to protect a circuit whose regular current does not exceed 
10 amperes, but it should not burn at 10, but at a value higher 
than this. By a 10-ampere fuse is meant one that will at least 
carry that much current. The rated capacities are 10, 15, 20, 30, 
40, 50, 60, 75, 100 amperes and the rated capacity is stamped on 
the face of one of the tips. Generator fuses are rated higher. 

Calculation of Sizes for Fuses. — The current that can be carried 
depends on the diameter of the fuse and not at all on its length, 
as will be shown. 

The number of joules produced by a current C in a resistance 
R in a time t is 

C 2 Rt. 



Wiring 641 

t nder the subject resistance, it was shown that 

R = a 
where 

p is the specific resistance of the substance, 
I is the length of the substance, 
and a is the area of cross-section. 

If the conductor is round 

or the number of joules in time t becomes 

If p is expressed as the resistance per cubic centimetre or rather 
the resistance .of a conductor one centimetre long and one square 
centimetre in cross-section, then I and d must be expressed in 
centimetres. 

The amount of heat radiated from the fuse depends on the 
material, on the initial temperature, on the melting point, on the 
surface available for radiation and on the time. 

The surface of the fuse is 

irdl sq. cm. (2) 

If the radiation per square centimetre per degree rise of tem- 
perature per second is known, the total amount radiated becomes 
known. For lead this is about .001 joule, or the total amount of 
heat radiated in time t, till the melting point is reached, 

.00l7rdlt(T—T f ). (3) 

T = melting point, 

T' = original temperature of fuse. 

When current flows through the fuse, if the heat is not radiated 
as fast as produced by the current, its temperature will rise, and 
at any time if radiation equals that produced, the temperature will 
remain stationary. If not, the temperature will go on increasing 
until the melting point is reached, and just at that instant it can 
be assumed that the number of joules produced by the current is 



64? Naval Electricians' Text Book 

equal to the radiation from the fuse, which it would he if the tem- 
perature remained stationary at the melting point. C could have 
such a value that this condition could exist, and any slight increase 
in C would destroy the equilibrium. At the instant (1) = (3) or 

-^ = .001irdlt(T--T'), 

an expression both independent of the length I of the fuse or the 
time t, as they are both common factors. Solving for d, we have 



Tr 2 .001(T—T) 

in which all values are known and d may be calculated. 

A rule for finding the diameter of a fuse is given similar to the 
above 



=©' 



d = 

where 

C = current in amperes, 

d = diameter in inches, 

and K = a constant, depending on the material. 

For lead K = 1379, and for half and half solder K = 1318, and 

for copper K = 10,244. 

Multiple Fuses. — Two fuses in multiple will carry twice as much 
current as one if they are in all respects alike, and so placed that 
the heating of one does not affect the other. Two fuses twisted 
together will not carry as much current as if they are apart, for the 
radiation in the twisted fuse is less and consequently the tempera- 
ture will be raised quicker. 

In making multiple fuses to carry a desired load, the factor, 
length, enters into the calculation, for different currents are to be 
carried, and the fall of potential being the same, the currents are 
proportional to the lengths. The absolute lengths of the fuses are 
not required but they must bear a certain ratio to each other. 

Suppose it was desired to make a copper fuse to protect a current 
of 250 amperes, by a No. 14 B. & S. copper wire. This size copper 
will carry 166 amperes before fusing, leaving the difference 84 
amperes to be carried by another fuse in multiple. The cross- 



Wiring 643 

section and specific resistance being the same, E:R':;l:V and the 
fall of potential being the same. CR = C'R', or 

R: R' :: C : O 

R : R' :: I : V 

G : (T : : V : I 

166 V 

If one fuse is made 1.66 inch in length, the other must be .84 
inch or some proj)ortion of these values. 

Fuse Shapes. — The fuses for non-water-tight receptacles, wall 
socket or receptacle plugs are of plain fuse wire of 3-ampere 
capacity. The fuses for branch junction boxes are of the copper- 
tipped glass-tube type. The fuse wire is enclosed in a glass tube 
fitted with copper tips, to which the fuse wire is soldered. The 
fuse goes through small holes in the copper tips, the latter being 
cemented to the glass tube. The capacity of the fuse is 3 amperes. 

The circuit fuses on the switchboard are of commercial copper- 
tipped pattern with slots in tips at right angles to each other. The 
length of fuse wire must be at least 1 inch. These fuses are 
ribbon-shaped. 

Fuses for generator circuits are of commercial copper-tipped pat- 
tern, 2-j- inches from center to center. These are ribbon-shaped, 
half circular in form. Bated capacities of dynamo fuses are 25, 50, 
75, 100, 200, 300, 400, 500. The rated capacity is stamped on one 
of the lugs. 

When a circuit requires a fuse larger than 100 amperes, a gener- 
ator fuse is used. 

When a generator fuse greater than 500 amperes is required, two 
fuses of equal capacity are mounted in parallel. 

Fuse wire or wire from which fuses are made is furnished on 
spools, wound like cotton, for convenience in cutting off any de- 
sired length. It is generally in spools of 3, 10, 20, 40, 60 and 100 
amperes, above which, completed fuses are used. 

Circuit Breaker. — The function of this piece of apparatus is well 
defined by its name, being a contrivance to break a circuit in case 
the current rises above a certain fixed value, acting for the same 
purpose as an ordinary safety fuse; to interrupt a circuit before 



644 Naval Electricians' Text Book 

the current becomes so great as to become dangerous on account of 
the heat produced. 

They are placed directly in the circuit to be protected and consist 
of a double-pole switch which when closed is held in place by a 
trigger against the tension of a very strong quick-acting spring. 
In the circuit on the breaker is an electromagnet surrounding an 
iron core which, as the magnet is energized by the current, is pulled 
into the hollow of the coil, the amount of the pull depending on 
the current. As the core is attracted, it is arranged to trip a 
release trigger, which releases the catch holding the spring, and 
the latter throws out the switch arms, breaking the circuit. The 
current for which the release may be effected may be varied by 
moving by hand the position of the plunger before current is turned 
on. A small index shows for what current the breaker is set, that 
is, for what current the switch arms will be released. 

Circuit breakers are placed in circuits that are liable to a sudden 
fluctuation in current, and in currents too great to be protected by 
ordinary safety fuses. If fuses were placed in search-light circuits, 
they would be continually melting owing to the high rise of cur- 
rent at intervals and necessitating constant renewals, an operation 
requiring much care and practice. When the circuit is broken by 
the circuit breaker it is only necessary to throw it in again by hand, 
the work of an instant. They can be used in the place of ordinary 
switches in circuits carrying heavy currents, for they can be oper- 
ated at will by hand and have the advantage of automatically 
opening in case of any sudden rise in current. 

The contact pieces, both on the switch arms and on the base of 
the switch, are made of block carbon, the carbons pressing against 
each other when the circuit is closed. This prevents the contacts 
from being burned away by the arc formed in breaking, which 
would soon be the case if they were of copper, on account of the 
low-fusing temperature of copper. 

In some forms of circuit breakers, the switch arms are made to 
act independently, each having its electromagnet device and trip- 
ping mechanism. 

Location of Fuses and Circuit Breakers. — Every precaution is 
taken in ship installation to guard against excessive currents, 



Wiring 645 

whether from short circuits, grounds, leaks or whatever cause. 
Every part of the installation is protected, each main generator, 
each circuit, each motor, or motor generator, each search or arc 
light and each individual incandescent lamp. There are main 
fuses or circuit breakers on the main switchboard to protect the 
generators, each lighting or power circuit is protected on the switch- 
board and each lamp on a circuit and each motor is separately pro- 
tected. The fuses for the incandescent lamps are placed in the 
junction boxes from which the branches are led. In certain places 
like the engine or fire-rooms, where the junction boxes would be 
likely to be installed in inaccessible places, they give way to distri- 
bution boxes, which are practically combinations of ten or twelve 
junction boxes, all the branches leading from these boxes. They 
are installed in accessible places, where all the fuses can be readily 
examined or replaced. As an illustration of the protection given, 
that from a generator to a small portable ventilating fan may be 
cited. There is the main fuse or circuit breaker between the gen- 
erator and main switchboard, then if there is a distribution board, 
there is a fuse between that and the main switchboard. The circuit 
on which the fan is installed is fused on the bus bar of the distri- 
bution board. At the junction box from which the fan leads there 
is a fuse. From the junction box the conductor leads to a receptacle 
which contains a fuse, and into this screws the plug from which 
leads the double conductor to the fan. This plug is also fused, 
making six fuses or circuit breakers in all between the generator 
and the fan, the safety appliances, of course, decreasing in size as 
the current falls off from that of the main generator, possibly 800 
amperes, to that of the fan, .8 ampere. 

Three-Wire System. 

Before leaving the subject of wiring, brief mention will be made 
of the three-wire system, which has been installed on two of our 
battleships, the Eearsarge and Kentucky. 

In this system, two generators are used, being connected in series, 
as indicated in Fig. 290, a and b representing the terminals of 
the two machines, the negative terminal of a being connected to 



646 Naval Electricians' Text Book 

the positive terminal of b, and from this connection a third wii 
leads out from the machines, following the lead of the ontside mab 
c and d. 

The lights are not taken directly from the mains leading froi 
the machine or switchboard, but from mains fed by feeders as 
usual in the feeder system, but the above illustration is made to 
illustrate the principles involved. 

The three mains run along together throughout the part of ship 
to be lighted, and as nearly as possible an equal number of lights 
is taken from each side; that is, from the outside positive to the 
middle or neutral wire, and from the outside negative to the 
neutral wire. 




Fig. 290. — Three-Wire System. 

The generators being in series, the difference of potential from 
c to d is twice that from c to e or of one generator. The effect of 
having practically two lamps in series, when one on each side of 
the neutral is burning, is to have a double E. M. F. and a double 
resistance, so the current through each is the same as though it 
were connected up on the ordinary two- wire system, with the E. 
M. F. of one machine and the resistance of one lamp. The result 
of this combination is to give the same current, consequently the 
same light, with the saving of one length of conductor. 

If there were an equal number of lamps on each side of the 
neutral burning, it is evident that the neutral wire would have no 
current at all, from which fact it derives its name, neutral. If 
there are an unequal number of lamps burning on the two sides, 
the neutral wire would carry the current which represented the 
difference between the total current on one side and the total cur- 
rent on the other. It is presumed that at least half as many lamps 



Wiring 647 

on one side would be burning as on the other, and it is the general 
practice to make the neutral wire of half the carrying capacity of 
the two outside wires. If, however, it is contemplated at times to 
use one generator as on the two-wire system, then the neutral wire 
would necessarily have to be of the same size as the other wires. 

Using one generator on the two-wire system detracts somewhat 
from the advantages of this system, one of which is the saving 
effected in the copper. To give the same illumination, two gener- 
ators running in the three-wire system effect a saving of about three- 
eights of the total copper used in the mains compared with that 
used with two generators on the two-wire system. If x represents 
the cross-section of the outside wires, and is used as a measure of 
their carrying capacity, the total wire used with the two generators 
two-wire system would be represented by lx, and on the two 
generators, three-wire system by 2\x, or a saving of l^x or f of ±x, 
the total amount. Where large areas are to be illuminated, this 
saving in copper would be considerable, but the saving is con- 
siderably reduced if the two-wire system is to be used, as is the 
case on shipboard. 

The other principal advantage of this system, as used on ship- 
board, is the increased E. M. F. ; from the standard voltage of 80 
as installed on those ships, there is available 160 volts for use on 
fast-running motors. The voltage from one outside to the neutral 
can be used for the slow-speed motors, and from the two outsides 
for the fast speed ones, or combinations can be made, the fields being 
excited either by one or the other, and the armature current taken 
with either voltage. 

Example of Three -Wire Circuit. 

In a three-wire system, with 160 volts between the outers, the load 
on the positive side consists of 40 5-c. p. lamps, 40 16-c. p. lamps and 
8 32-c. p. lamps; on the negative side the load is 20 5-c. p. lamps, 60 
16-c. p. lamps and 6 32-c. p. lamps. What is the magnitude and direction 
of the current in the neutral wire? Each lamp requires 3 watts per 
candle power. 

If the neutral becomes disconnected from the generators, what is the 
voltage across each set of lamps? 

Ans. 3.35 amperes, away from machines. 
83 volts across + side. 
77 volts across — side. 



CHAPTER XXVIII. 

WIRING APPLIANCES AND FIXTURES. 

Wiring appliances are of three general classes: conduit wiring 
appliances, wiring appliances (water-tight) for use with molding 
and wiring appliances (non-water-tight). 

In general all wiring appliances consist of a cast composition 
box, a sheet-brass cover, -a sheet-rubber gasket (for water-tight 
appliances) and an interior fitting on a porcelain base. 

Standard Conduit Wiring Appliances. 

Junction boxes: 

Feeder, 3-way branch, 

Main junction, 4-way branch. 

Switches : 

5-ampere single-pole, 

5-ampere single-pole with hood, 

25-ampere double-pole, 

50-ampere double-pole, 

100-ampere double-pole, 

50-ampere double-pole, double-throw. 

Receptacles : 

5-ampere, 

5-ampere with hood. 
Combination switch and receptacle: 

5-ampere, 25-ampere, 

5-ampere with hood 25-ampere with hood. 

Distribution boxes: 

8-way, 
12-way. 

Water-tight boxes: 

For l^-inch conduit, 
For l^-inch conduit, 
For 1-inch, %-inch, and %-inch conduit 



1 



Wiring Appliances and Fixtures 649 

Standard Appliances for Molding (Water-Tight). 

Junction boxes: 

Feeder, 3-way branch, 

Main, 4-way branch. 

Switches : 

5-ampere single-pole, 

25-ampere double-pole, 

50-ampere double-pole, 

100-ampere double-pole, 

50-ampere double-pole, double-throw. 

Receptacle: 

5-ampere. 
Combination switch and receptacle: 
5-ampere, 
25-ampere. 

Standard Appliances (Non-Water-Tight). 

Switch. 
Receptacles : 

Key, 

Keyless, 

Porcelain base. 

Sockets : 
Key, 
Keyless, 
Instrument lamp. 

In addition the general term " wiring appliances " also includes 
fuses, gaskets, stuffing tubes, box tubes, terminal tubes, conduit and 
molding. 

Conduit Wiring Appliances. 

All boxes for conduit wiring consist of a cast composition, box 
shape, fitted with a brass cover through which is a hole covered by 
a screw cap. Cover is secured to box by screws through a sheet- 
rubber gasket. The interior fittings rest on a porcelain base, 
secured to the bottom of the box through sheet mica. The sides 
and ends of the boxes are bossed and are threaded to receive the 
conduit according to the use for which the box is intended. The 
boxes are fitted with lug feet by which they are secured in place 
bv screws. 



650 Naval Electricians' Text Book 

Junction Boxes. — These are of two sizes, the smaller used when 
wire is 30,000 c. m. (twin conductor) or smaller. They are fitted 
for conduit connection on both ends and sides. 

Feeder Junction Box for Double Conduit. — These are used when 
wire size is in excess of 60,000 c. m. (twin conductor) and each leg 
of circuit is run in a separate conduit. These boxes are used for 
wire sizes up to 157,563 c. m. 

5-Ampere Switch, Single-Pole, Box. — Fitted to be inserted in the 
conduit line, and to take either -J or f-inch conduit, with a maxi- 
mum wire size 9016 c. m. (twin conductor). Box cover fitted with 
switch stem, the stem made water-tight by stuffing-box, packing 
ring and gasket. 

25-Ampere Switch, Double-Pole, Box. — Fitted to take 1-inch con- 
duit with maximum wire size of 30,000 c. m. (twin conductor). 
Fitted with screw cap over switch when not in use. 

50- Ampere Switch, Double-Pole, Single or Double-Throw, Box. — 
Fitted for lj-inch conduit, otherwise like preceding box. Box for 
100-ampere switch is same as for 50 amperes. 

5-Ampere Receptacle Box. — Fitted to take a J or f-inch conduit, 
all receptacles being threaded on one side of the box only for con- 
nection to the conduit. Fitted with cover for use when receptacle 
plug is not in use. 

5-Ampere Switch and Eeceptacle Box. — Same as preceding and 
fitted with switch handle like 5-ampere switch. 

25-Ampere Double-Pole Switch and Receptacle Box. — Fitted with 
two holes, one for receptacle, one for switch, with covers; otherwise 
like 25-ampere switch. 

Distribution Boxes, 8-Way and 12-Way. — These are large com- 
position boxes, for taking off eight or twelve branch circuits. The 
ends are threaded for 1-inch conduit, maximum wire size 30,000 
c. m. (twin conductor) and the sides for -|-inch conduit for branches, 
maximum wire size 4107 c. m. The interior fitting consists of a 
fuse board panel, so arranged that each branch is fused. Fuses 
used are the same as in the ordinary junction boxes. Current- 
carrying parts are made of sheet copper, mounted on a slate base, 
which rests on a hardwood block. The cover has two rectangular 
holes directly over the fuses, these holes covered and made water- 



Wiring Appliaxces axd Fixtures 651 

tight by means of two fuse doors hinged together. The arrange- 
ment is such that the fuses may be examined or replaced by 
opening one fuse door without removing the cover. 

Water-Tight Boxes. — These are used to water-tight the inside of 
conduit. Each size of conduit requires special size stuffing tube. 
The inside diameter of all tubes is identical with inside diameter 
of conduit. 

Molding Wiring Appliances. 

All wiring boxes are cast from composition metal with certain 
standard dimensions, and fitted with covers of sheet brass, which 
are secured to the boxes by screws through a gasket of 2-ply cloth 
insertion sheet-rubber packing. All except main junction boxes, 
which have plain covers, have a hole in the center of the covers, to 
which nipples are secured on which screw threaded caps. 

All wires entering these appliances do so through stuffing tubes, 
placed on the sides or ends of the boxes. These tubes are of two 
sizes, one called large size, the other small size. The maximum 
wire size for the large size is 157,563 c. m. and for the small size 
50,000 c. m. These stuffing tubes consist of the tube proper se- 
cured to the box, a screw gland screwing down on a gland washer 
stamped from sheet brass which in turn presses on a conical rubber 
gasket, making a water-tight joint between the tube of the box and 
the insulation of the wire. 

Main junction boxes are fitted with two large stuffing tubes in 
each end. 

Feeder junction boxes are fitted with two large stuffing tubes in 
each end and two large stuffing tubes in one side. 

Thre-way junction boxes are fitted with two large stuffing tubes 
in each end and two small stuffing tubes in one side. 

Four-way junction boxes are fitted with two large stuffing tubes 
in each end and two small stuffing tubes in each side. 

5-Ampere Switch, Single-Pole, Box. — Wires are led into box 
through two small stuffing tubes in each end. Is fitted with 1-inch 
hole in cover for switch stem, which is fitted with a stuffing-box, 
packing ring and gasket. A water-tight cap screws down over 
stuffing-box. 



652 Naval Electricians' Text Book 

25-Ampere Switch, Double-Pole, Box. — Wires are led into box 
through two large stuffing tubes in each end. The cover has a 
1-inch hole over switch handle, covered by a water-tight cap, which 
is removed when shipping handle for operation of switch. 

50 and 100-Ampere Switch, Double-Pole, Box. — Wires are led 
into box through two large stuffing tubes in each end and the same 
on one side. Cover is fitted as for 25-ampere switch. 

50-Ampere Switch, Double-Pole, Double-Throw, Box. — Wires are 
led into the box through two large stuffing tubes in each end and 
the same on one side. In all other respects they are like the 50- 
ampere box. 

5-Ampere Receptacle B©x. — This is in all respects like the 5-am- 
pere switch box except in hole in cover, which has a cap fitted as 
in the 25-ampere switch, double pole. 

5-Ampere Switch and Receptacle Box. — This is in all respects 
like the 5-ampere switch box, single pole, excepting cover, which has 
an additional hole fitted as in the 25-ampere double-pole switch. 

25-Ampere Double-Pole Switch and Receptacle Box. — This is in 
all respects like the 25-ampere switch, double pole, excepting cover, 
which has two additional holes for single-pole receptacle plugs. 
All holes are fitted with caps the same as for the 25-ampere switch, 
double-pole box. 

All the above boxes are made according to standard dimensions 
which differ for each class of box. 

Interior Fittings. 

The interior fittings for all wiring appliances of a similar name, 
whether for conduit or molding, are identical. All consist of 
copper-carrying conductors secured to porcelain bases which are 
screwed to the bottom of the boxes, a layer of mica being inter- 
posed between the porcelain and metal of the box. 

For feeder boxes they consist of double-pole conductors, fitted 
for one branch. Branch is fused with copper-tipped commercial 
fuses, and in addition is fitted with copper connecting strips to 
bridge fuse gaps when desired. Fuses are fitted on mica cups clear 
of the conductors. Binding strips are large enough to take wires 
as large as 157,563 c. m., navy standard. 



Wiring Appliances and Fixtures 653 

For main junction boxes they consist of double-pole, double- 
branch conductors, fitted for two branches. Fuses are in glass 
tubes with circular metal tips, secured by spring clips. Binding 
strips are large enough to take wires as large as 60,000 c. m., navy 
standard. 

For 5-ampere switch, single-pole, boxes they consist of double- 
pole conductors, with one broken by a switch, the handle for which 
is on the outside of box. Switch is quick break with contact springs 
of phosphor bronze. Binding strips are large enough to take wires 
as large as 9016 c. m., navy standard. 

For 75-ampere switch, double-pole, boxes they consist of double- 
pole conductors, both broken by switches, which are quick-break 
with contact springs of phosphor bronze. Switch is fitted without 
a handle, but operated by a standard wrench. Binding strips are 
large enough to take wires as large as 60,000 c. m., navy standard. 

For 50-ampere switch, double-pole, boxes they consist of the 
same general design as the 2 5-ampere switch, but with strips large 
enough to takes wires as large as 157,563 c. m., navy standard. The 
fittings for the 100-ampere switch, double pole, are the same with 
exception that conductors are larger. 

For 50-ampere switch, double-pole, double-throw, boxes they 
consist of double-pole conductors, both broken by quick-break 
switches, double pole, in order to make contact from a pair of side 
wires to either pair of end wires. Switch is operated by wrench. 
All parts are large enough to carry 40 amperes without perceptible 
heating. 

For 5-ampere receptacle box they consist of double-pole con- 
ductors, one end of each fitted to receive the wires, the other end 
of each secured to phosphor bronze clips for securing receptacle 
plugs. One end of these clips is secured to the conductor, the other 
is free. Binding strips are large enough to take wires as large as 
9016 c. m., navy standard. 

For 5-ampere switch and receptacle boxes they consist of fittings 
the same as for the 5-ampere receptacle with the following excep- 
tion : One leg of the conductor leading to the receptacle is broken 
by a switch in all respects like the 5-ampere switch. 

For 25-ampere combination switch and receptacle box they con- 



654 Naval Electricians' Text Book 

sist of fittings the same as for the 25-ampere switch with the fol- 
lowing exception: Only one end of the conductors are fitted to 
receive wires, the other end of each conductor is fitted with re- 
ceptacle clips like those for the 5-ampere receptacle. 

All switches are " on " when the switch handle is lengthwise of 
the box and "off" when they stand across the box. In those 
switches turned by a standard wrench, the wrench and end of switch 
stem are so designed that the former cannot be shipped unless it is 
put on lengthwise of the box when the switch is " on " and cross- 
wise when it is " off." 

Non-Water-Tight Wiring Appliances. 

Switches. — The fittings of the switch are mounted on glazed vit- 
rified porcelain, and the switch proper is single pole, snap and 
quick break, with springs of phosphor bronze. The stem and 
handle of switch are of metal, and made to turn in one direction 
only — to the right. Capacity of switch 10 amperes. 

Sockets. — The socket proper of key or keyless sockets is made 
of a close helical spring of 6J turns, No. 11 B. & S. phosphor 
bronze wire, the free end turned to form a small loop. One con- 
ductor is secured to this spring, the other to a central contact piece 
of sheet phosphor bronze. Sockets fit standard 16, 32 and 150- 
candle-power lamps. The fittings are secured to a porcelain base 
and covered with a shell of sheet brass made in two pieces. The 
key for key sockets is of insulating material, usually hard rubber. 
The circuit for the key socket is broken by a snap arrangement 
giving a clean, quick break. 

Receptacles. — The fittings of the key and keyless receptacles are 
mounted on round porcelain bases, which are arranged for fusing 
both legs of the circuit. The socket is of the ordinary commercial 
type, covered with a brass shell. The key for key receptacle is 
like the one for the key socket. The porcelain base receptacle is 
mounted on a porcelain base, the socket the same as the key and 
keyless sockets with the helical spring. This receptacle is not fused. 

Instrument Lamp Socket. — This is for use with instruments as 
the battle order transmitters. It is of the helical spring type of 
phosphor bronze wire. Terminals are fitted to take wires as large 
as standard double conductor 7-22 B. & S. wire. 



Wiring Appliances and Fixtures 655 

Conduit. 

Conduit consists of the following types : 

1. Steel, enameled. 

2. Brass, enameled. 

3. Flexible. 

The steel and brass enameled conduits conform in their metal 
parts to the dimensions for standard steam, gas and water pipes. 
The}' are the following sizes, inside measurement: J", f", 1", 1J", 
1J", 2", with lengths of 10 feet for steel and 12 feet for brass. 
The enamel is put on in not less than three coats, baked on, inside 
and out, and is not to be affected by moisture, acids, alkalies or a 
temperature of 100° C. Sabin's baking enamel is frequently used. 

Fittings. — The fittings for steel-enameled conduit are of steel, 
wrought, malleable or cast iron, for brass-enameled conduit they are 
of brass or the " beaded malleable " pattern. The following fittings 
are used with the conduit, steel or brass, conforming to the dimen- 
sions of the conduit : 

Elbows bent 90° in equal legs, externally threaded on both sides. 

Outlet elbows 90°, similar to steam-pipe elbows, both ends 
threaded internally. 

Outlet elbows 45°, similar to above, with both ends threaded 
internally. 

Nipples. — Externally threaded on both ends. 

Couplings. — Similar to regular pipe couplings, internally 
threaded, with both ends right-hand thread, or one end with right 
hand thread and one with left-hand thread. 

Unions. — Similar to regular pipe unions. 

Couplings, Reducing. — Similar to regular pipe couplings, inter- 
nally threaded, right hand. 

Plugs. — Similar to regular pipe plugs, right hand. 

Bushes. — Similar to regular pipe bushes. 

Flexible Conduit.— This is used in sizes of 1", 1J", IV, 2", 2^", 
2J", 3" inside measurement. It is made of rubber-lined hose, 
double cotton. 



65 G Naval Electricians' Text Book 

Molding. 

Molding consists of three parts; that part containing the wire 
gutters is known as the molding, the part npon which the molding 
rests is called the baching strip and that which covers the molding 
is the capping. 

When run over hardwood surfaces, molding is of the same ma- 
terial and finish as the surrounding woodwork. In all other cases, 
it is of thoroughly seasoned white pine, coated with white lead 
before being secured in place. 

The backing strip is used to cover all rivet and bolt heads, nuts, 
etc., and to make a smooth surface for the molding. 

Molding is made with one, two or three gutters. 

Gaskets. 

All gaskets used in the various kinds of water-tighting appli- 
ances are made of vulcanized rubber compound, containing only 
pure Para rubber, mixed with mineral matter and sulphur. 

The compound contains at least 60 per cent by weight of rubber 
gum, and sulphur not less than 4-J per cent nor more than 5-J per 
cent of the weight of the rubber gum. All the sulphur must be 
combined with the rubber, there being no free sulphur in the 
compound. 

Gaskets are made of eight types, each of which is designated by 
a letter. They are all of the same general shape, the different types 
being distinguished by their dimensions. A description of one 
type is given. 

Type A. — The shape is that of two truncated cones of unequal 
heights joined base to base, diameter top 1\ inch, bottom 1-^- inch, 
diameter of cone bases 1J inch. The shorter cone tapers from 
smaller to larger diameter in a height of -J inch and the larger cone 
is a height of j| inch, total length of gasket ^| inch. The gasket 
is perforated with a central hole the full length of the gasket. 
The size of the hole is designated by a number signifying the diame- 
ter in thirty-seconds of an inch. The numeral zero placed after the 
letter signifies that the gasket is solid. This type is designated 
as A30, A36, A0, etc. 



Wiring Appliances axd Fixtures 



657 



In certain forms of gaskets which are made with two or three 
holes, the designation is by a repetition of the letter as man}- times 
as there are holes, followed by a number specifying the diameter of 
the holes in thirty-seconds of an inch. Thus type C, with two 
holes -if inch in diameter, would be designated as (7(718. If more 
than three holes are used, the word spelling the number of holes is 
added, followed by the numeral for size. Thus G sixteen — 8 would 
mean type G gasket, with 16 holes, each-^- inch in diameter. 

If a gasket with oval hole is used, the letter is followed by two 
numerals, indicating the two diameters in thirty-seconds of an inch, 
thus (716-10 would mean a gasket of type C, with a hole -|f inch 
by y inch. 




Fig. 291. — Single Bracket Fixture. 



Fixtures. 

Fixtures are referred to as regular fixtures and lanterns. Regu- 
lar fixtures are those that are secured permanently in place in 
various compartments and spaces, and intended for general illumi- 
nation. They include: 

Regular Fixtures. 



Bracket light, single or double, 
Bulkhead fixture, 
Bunker fixture, 
Ceiling fixture, No. 1, 
Ceiling fixture, No. 3. 



Ceiling fixture, commercial, 

Deck fixture, 

Drop light, 

Overhead bunker fixture. 



658 



Naval Electricians' Text Book 






Bracket Light. — The bracket light is used for side lighting in 
officers' quarters and offices. The single-bracket light is illustrated 
in Fig. 291. All brackets are finished in dark bronze and are 
buffed before being bronzed. 

This fixture is secured to a brass base with a cast boss in the side 

into which the conduit screws. 
There are two smaller bosses 
which may be tapped for the con- 
duit of the switch wires. 

The double-bracket light is 
similar to the single type, but has 
two arms set about 90 degrees 
apart. Fluted shades are used 
with these fixtures. 

The bulkhead fixture, deck fix- 
ture and drop light are all simi- 
lar in construction, and are alike 
with the exception of their bases. 
A deck fixture is shown in Fig. 
292. 

In general it consists of a metal 
flanged conical base, fitted with 
screw-thread, on which screws 
against a washer a clear glass 
globe. This globe encloses the 
lamp which fits into a socket se- 
cured to the base, and around the 
globe is fixed a metal guard. All 
metal parts are finished with a 
dark bronze. 

The base for the deck fixture 
has a boss tapped for the conduit 
and two vertical lugs by which it is secured to the deck. 

This fixture is secured overhead under the deck, and in such 
places as passages, lower decks, under gratings in fire-room and 
engine-rooms, and in general where there is good head room. 
The drop light has a conical base, tapped at its apex for the con- 




Fig. 292.— Deck Fixture. 



Wiring Appliances and Fixtures 659 

duit. This fixture replaces the old steam-tight globe-fixture, and 
finds particular use for lighting fire-rooms from overhead, steam 
and gauge glasses, etc. 

The bulkhead fixture replaces the old form of bulkhead fixture 
used with molding. Its base is similar to that of the drop light 
in having a central boss tapped for the conduit, but in addition it 
has two side lugs cast in one with the base by which it is screwed 
to the bulkhead. 




Fig. 293. — Bunker Fixture. 

It is used entirely for side lighting, and in places for overhead 
lighting where the drop light would require too much head room. 
It is used on the berth deck, for standing lights, for lighting upper 
decks and under bridges, and in the engine and fire-rooms. It is 
also installed in places where formerly was used the ceiling fixture 
No. 2 which is now not a standard fixture. 

Bunker Fixture. — As the name implies this style of fixture is 
used for lighting coal bunkers. It is shown in Fig. 293. In gen- 
eral it consists of a cylindrical casting forming a box in which the 
lamp is secured, the top of the casting having a boss tapped for the 
conduit. The back of the casting is covered by a plate with stiffen- 



660 



Naval Electricians' Text Book 



ing rings, in the center of which is a hole ordinarily covered by a 
screw cap by which the condition of the lamp may be seen. 

The front of the casting is covered with a plate of glass 1-inch 
thick, over which a follower ring is bolted to hold the glass in place, 
and which is provided with four vertical guard ribs to protect the 




Fig. 294. — Ceiling Fixture, No 



glass from the coal. The fixture is put in place from the outside 
of the bunker and is secured by J-ineh bolts. 

The overhead bunker fixture is somewhat similar to the ordinary 
bunker fixture, but is fitted to be secured overhead in a bunker and 
not through a bulkhead. It lights the bunker more efficiently but 
has the disadvantage of requiring the glass face to be removed 
before a lamp can be replaced. 



Wirixg Appliances axd Fixtures 661 

Ceiling Fixture No. 1. — Fig. 294: shows a fixture of this type that 
was standard for a number of years. In the present standard, the 
open fancy work on the base is replaced by a brass casting with an 
interior boss, which is tapped for the conduit, and two extra bosses 
on the sides which may be tapped for conduit switch wires. The 
lamp screws in a standard socket secured to the base and is sur- 
rounded by a globe, frosted on the inside. 




Fig. 295. — Ceiling Fixture, Commercial. 

This fixture is used extensively in cabins and officers' mess-rooms 
where there is plenty of head room. 

Ceiling Fixture No. 3 is somewhat similar to Xo. 1, with the 
exception that the lamp is mounted horizontally, and the globe is 
flatter and of clear glass. The interior of the base is painted 
white. It is used in open spaces for overhead lighting. 

Ceiling Fixture, Commercial. — This type is shown in Fig. 295. 
In addition to the details shown it has a cast-brass base fitted with 
the bosses which are taped for conduit and conduit switch wires. 

All ceiling fixtures are bronzed, but the bases may be painted to 
correspond to the woodwork. 



662 



Naval Electricians' Text Book 



Lantern Fixtures. 

These are movable fixtures and secured to convenient receptacles 
by flexible conductors. They include : 
Battle lantern, Desk light, 

Deck lantern, Magazine lantern, 

Cargo reflector, Portables, water-tight and non-water-tight. 



Battle Lantern. — This is a hand 
lantern used in night action around 
guns, ammunition hoists, passages, 
etc. A type that was the standard 
for some years is shown in Fig. 296. 
It consists essentially of a cap sup- 
porting the lamp socket and which 
also forms the support for a cylin- 
drical glass globe surrounding the 
lamp. Around the globe is fitted a 
wire guard and inside of which is a 
metal shield. One-half of this shield 
is fixed and the other half may be 
turned so as to completely shut off 
all light or it may be turned so that 
light will be thrown over half a cir- 
cumference. 

The present standard differs some- 
what in construction, although the 
general features remain the same. 
The cap is made so that the outlet 
for the conductor leads in horizon- 
tally instead of vertically, and all 
parts, including the top and bottom 
pieces, handle and guard, are heavier 
to withstand more severe usage. It 

is also fitted with a hinged door on the bottom to shield the light in 

that direction. 

The deck lantern is in all respects similar to the battle lantern 

but is not fitted with the metal guard. It is used where open 

lights are required on the upper decks or bridges. 




Fig. 296.— Battle Lantern. 



Wiring Appliances and Fixtures 



663 



Cargo Reflector. — This is shown in Fig. 297. It consists of a 
dome-shaped brass reflector, covered by a guard of wire mesh. The 
inside of the reflector is painted white. In the reflector are 
mounted four keyless sockets, holding four lamps. These sockets 




Fig. 297.— Cargo Reflector. 



are all wired in parallel and their ends soldered to the flexible con- 
ductor which leads into the top through a stuffing gland. The 
figure shows curved arms holding the sockets, but in the present 
standard the arms are done awav with and the sockets are mounted 



GO-i 



Naval Electricians' Text Book 



directly on the base, and are inclined about 45 degrees to the 
vertical. 

This lantern finds extensive use as gangway lights, and for light- 
ing coal barges or lighters where special amount of light is required. 

Desk Light. — The fixture that was standard for some years is 
shown in Fig. 298. The present standard is very similar except 






Fig. 298.— Desk Light. 



that the stand is somewhat lower, and the curved support is carried 
up on each side of the socket and lamp and the light is not fitted 
to be removed. The light can be swung in its supports and clamped 
in any position. It is wired with double conductor, silk, and is 
used in officers' quarters and offices. 



Wiring Appliances and Fixtures 



6Q, 



Magazine Lantern. — This is shown in Fig. 299 and is used for 
lighting magazines and shell-rooms. It is placed in a permanent 
box built in the ship, which is provided with openings covered by 
glass through which the light niters. It is composed of a rectangu- 




Fig. 299. — Magazine Lantern. 



lar brass box, bronzed, about 18" X 8", provided with circular open- 
ings in each of its four sides. Two lamps are wired in each lantern, 
the conductors entering the top through stuffing glands. Two 
sliver-plated reflectors are furnished with each lantern and they 
may be hung as desired to reflect the light in the required direction. 



666 



Naval Electricians' Text Book 



Portables. — These are of two types, known as water-tight and 
non-water-tight. The water-tight type is il- 
lustrated in Fig. 300. It is similar in con- 
struction to the general steam-tight globe 
fixtures of the bulkhead and deck type, but is 
provided with a handle for ease in manipula- 
tion, and a hook by which it may be hung up. 
It is wired through the handle through a 
stuffing gland, and the latest type is fitted 
with a phosphor bronze spring, about 4 inches 
long, surrounding the conductor. This ends 
in a brass casting which is fitted with a sec- 
ond stuffing gland. This spring protects the 
insulation of the wire and prevents abrasion 
by obviating any sharp turns of the con- 
ductor where it enters the handle. 

This portable finds use in engine and fire- 
rooms, coal bunkers, double bottoms, etc., and 
in places where water or moisture is apt to be 
found, or where hard usage may be expected. 

The non-water-tight type is similar to the 
water-tight type, but is generally smaller and 
lighter in construction, and is not fitted 
with a water-tight globe. It is fitted with 
a ring at the top instead of a hook and the 
protecting spring for the insulation is left 
off. 




-Portable, 



Fig. 300 

Water Tight. 



Special Fixtures and Lanterns. 

Special fixtures and lanterns are those used each for some specific 
purpose other than general illumination and including the fol- 
] owing: 

Binnacle light, Peak lights, Telegraph fixture, 

Diving lantern, Range light, Top lantern, 

Blinker signal light, Side lights, Towing lantern, 

Masthead lantern, Signal lanterns, Truck light, 

Night signal lantern, Stay light, Turret-hood fixture. 



Wirixg Appliances axd Fixtures 667 

The binnacle light is used for illuminating the compass card in 
the binnacle. It consists of a cylindrical casing carrying a socket 
and lamp, and is provided with a handle by which it is lifted into 
or out of the opening in the center and top of the binnacle cover. 
It is wired through a stuffing gland on one side, the conductor lead- 
ing to a receptacle usually secured on the base of the binnacle. 
The light from the lamp shines directly down on the center of 
the card. 




Fig. 301. — Diving Lamp. 



668 Naval Electricians' Text Book 

The diving lantern is used under water when required by a 
diver. It is furnished with double conductors, and each wire of 
the conductor is connected to a 25-ampere receptacle plug. The 
lamp and conductor is illustrated in Fig. 301. A 25-ampere switch 
and receptacle is provided on each bow and quarter, and in long 
ships, extra outlets are provided. 




Fig. 302. — Masthead Lantern. 

The fixture consists of a cylindrical glass globe held by metal 
rods between two metal caps with water-tight joints. The metal 
cap contains the lamp socket which is wired through a metal rod 
and made water-tight by a stuffing tube. This metal rod acts as a 
handle to manipulate the light. For a short distance beyond the 
stuffing gland, the conductor is wrapped with iron wire to prevent 
the insulation from breaking near the stuffing gland. There is a 



Wiring Appliances axd Fixtures 



669 



screw connection through the outer cap to allow any moisture to 
be dried out. The fixture requires a conductor of a special make. 
The blinker signal light is a form of hand lantern used for wig- 
wag signalling and fitted with a sliding screen by which the light is 
cut off at will. 




Fig. 303.— Side Light Lantern. 



The masthead lantern and side-light lanterns are constructed to 
meet the requirements of the Eules of the Eoad. The present 
standards are very slightly different from those shown in Figs. 302 
and 303, principally in the method of securing them in place. 

The lenses used are clear Fresnel lenses of cut glass, each lens 
forming a quadrant. For the masthead light two of these quad- 



670 



Naval Electricians' Text Book 



rants are used, making exactly 180 degrees, while for the side lights, 
a single quadrant lens is used in each. The lenses are each built 
up in five sections, the central one being a piano convex lens, the 
outer sections on each side are circular prisms. 

The lenses for these lanterns are clear 
glass, but for the side-light lantern, colored 
screens, either red or green, are fitted just 
inside the lenses, to provide for the star- 
board and port lights. The lanterns are 
wired through stuffing glands — in a casting 
at the top of the lantern, and are fitted to 
take two 32-candle-power lamps, though 
only one is ordinarily used. The lamps 
may be renewed through a hinged door in 
the back of the lantern. 

For range lights, the regular masthead 
lantern is used in connection with a second 
one properly placed. 

For towing lights, a second masthead 
lantern is used with the regularly fitted one. 
For top lights for flagships, a lantern ex- 
actly similar to the masthead lantern is 
used. 

The night signal lantern is one of four 
used with the regular night-signalling in- 
stallation. It is illustrated in Fig. 304. It 
consists of two composition castings, one at 
each end, containing the stuffing glands for 
the conductors, and a top and a bottom 
piece into which the castings are secured, 
held together by side rods. Between the two end pieces are secured 
two 6-inch lenses with a diaphragm between them. The upper lens 
is red and the lower one is white. 

The signal lantern is illustrated in Fig. 305. The lens is in one 
piece, with the piano convex lens as the middle section, and prisms 
for the outer sections. The lens is protected by a metal guard. It 







Fig. 304.— Night 
Signal Lantern. 



Wiring Appliances axd Fixtures 



671 



is wired through a stuffing gland in a casting in the top piece for 
one lamp. The lenses are furnished in three colors, white (plain), 
red and green. The body of all the lenses is clear glass, the colored 
ones being obtained by flashing the colored glass on the interior of 
the clear lenses. 





Fig. 305. — Signal Lantern. 



Fig. 306.— Truck Light 



For peak lights, stay lights and stern lights, signal lanterns are 
used. 

The truck light is illustrated in Fig. 306. The lantern itself 
is very similar to that used for night signalling, and has the same 
size and style of lenses, the upper one red and the lower one white. 
It is supported on a heavy brass casting which fits on the mast 
truck. It is wired for a 32-candle-power lamp in each lens. 



672 Naval Electricians' Text Book 



The telegraph fixture is used to illuminate the dials of engine- 
room telegraphs. It is a 5-candle-power lamp mounted in a cylin- 
drical box, with the lamp socket on one end, the other end being 
covered with a thin sheet of mica, through which the light shines. 
This is mounted on a rectangular brass plate which fits in guides 
on the back of the telegraph. 

The turret-hood fixture is used to illuminate the drum of the 
telescopic sights for the turret guns. It consists of a metal casting 
as a base through which a 5-candle-power lamp is wired. Attached 
to the casting is a cylindrical casing surrounding the lamp, and the 
end of the casing is closed by a door. The light is thrown through 
the end of the casing into the sight hole, or it can be thrown on the 
telescopic drum by means of a sliding screen in the casing around 
the lamp. 






CHAPTEE XXIX. 
MEASURING AND TESTING. 

There are man}' laboratory methods for measuring electrical 
quantities and testing electrical machines, but on shipboard meas- 
urements are limited by the instruments furnished; these only 
being sufficient in a most general way for measuring the three 
electrical quantities of resistance, difference of potential and current. 

The instruments ordinarily furnished to ships for electrical 
measurements are voltmeters, ammeters, testing sets and magnetos. 
In addition, on some ships may be found ohmmeters, whose prin- 
ciple and use will also be described. 

Instruments. 

Every electrical effect has a cause, and the effects produced are 
made the basis of the construction of electrical instruments. The 
effects generally taken advantage of are those falling under the head 
of static, heating, chemical or magnetic. 

Of these effects, the last, that of magnetic, or electromagnetic, 
is the governing principle of the instruments furnished for use on 
shipboard. Instruments based on static, heating or chemical effects 
are used as standards to a greater or less degree and their principles 
will be briefly touched on. 

Electrostatic Effect. — If there is a difference of electrostatic 
potential existing between two conductors, they tend to attract one 
another. If one is freely suspended while the other is immovable, 
the suspended one in approaching the other may be made to carry 
a pointer which will indicate the difference of potential. Volt- 
meters made on this principle are for certain ranges the most accu- 
rate, as they absorb no current, and there is no fall of potential 
due to the instrument itself. 

Electrostatic voltmeters are made for measuring high potential 
difference and they are not usually suitable for measuring small 
voltages. Electrostatic voltmeters may be used to measure current 
by the fall of potential through a known resistance. 



674 Natal Electricians' Text Book 



to its 



Heating Effect. — The fall of potential in a conductor due 
own resistance represents a loss of energy of electric current which 
reappears as heat, and which raises the temperature of the con- 
ductor. The amount of heat developed may be measured, and 
from this the current producing the heat may be measured. 

The heat produced in a conductor causes expansion of the con- 
ductor in reference to other conductors through which the current 
is not flowing. This expansion may be measured and the tempera- 
ture thus found, and therefore the current measured which pro- 
duced it. In the Cardew voltmeter, the conductor consists of a 
wire of high resistance, three or four yards in length. The current 
that flows through this conductor is proportional to the E. M. F. 
at the terminals, and this current, owing to the heat produced, 
causes the conductor to lengthen. As the conductor expands, it 
sets in motion a train of wheels moving a pointer which indicates 
the difference of potential. 

Electrochemical Effect. — When a current passes through a liquid 
(not an elementary substance), the liquid is decomposed, part 
going to that conductor where the current enters the liquid, and 
part where the current leaves the liquid. If the electrodes and the 
electrolyte are prepared according to some standard specifications, 
the same current in the same time will always liberate the same 
amount of matter. This matter can be measured and therefore the 
current determined. 

This effect is very accurate and is used in this country as a stand- 
ard for measuring currents (see under Ampere). In its ordinary 
form it cannot be used as a voltmeter, nor directly as an ammeter, 
unless the current remains constant for the whole time. 

Magnetic Effect. — Several classes of instruments are made de- 
pending upon magnetic or electromagnetic effect. Some depend 
on the mutual attraction or repulsion of conductors carrying cur- 
rent due to the magnetic fields set up around them; others depend 
upon the reaction between a magnetic field due to some outside 
source and the magnetic field set up around a conductor carrying a 
current lying in that field, and still others depend upon the attrac- 
tion between a conductor carrying a current and the field induced 
by it in some soft-iron core. 



Measuring axd Testixg 675 

Siemen's Dynamometer. 

An example of the class of instruments based on magnetic 
effects is the well-known Siemen's electro dynamometer, which is 
of interest on account of its being used as a standard, and on 
account of its being adaj^table for either a voltmeter or an am- 
meter, or even indeed as a wattmeter. This dynamometer consists 
of two coils at right angles to each other, one being stationary while 
the other is free to revolve. The movable coil hangs from a thread 
secured to a spiral spring, which in its normal condition allows 
the coil to remain at rest perpendicular to the stationary coil. 
Current is sent through the two coils and the magnetic fields set up 
around the conductors tend to move the two coils so as to make their 
planes parallel. This tendency causes the movable coil to rotate 
against the tension of the spiral spring, and it comes to rest in a 
position determined by the relative strengths of the fields and that 
of the spring. The amount of twist given the spring in order to 
bring the movable coil back to its zero position is a measure of the 
current in the coils. The spring is twisted by means of a milled 
head which carries a pointer travelling over a scale which indicates 
the current. 

If both coils are made of a large number of turns of fine wire, 
it can be used as a voltmeter by connecting a high resistance in 
series with it. It still measures the current, but this is propor- 
tional to the E. M. F. at the terminals and the force is a measure 
of the E. M. F. 

This form of instrument could not be used on board ship, for it 
must be carefully leveled, and it is not direct reading, so it requires 
time and very careful handling, and is of not much use if the cur- 
rent fluctuates. It is of special value, though, for calibrating 
other instruments, and its permanence and reliability depends only 
on the spring, which experience has shown is practically un- 
changeable. 

The voltmeters and ammeters furnished for use on shipboard 
come under the second class given under the heading, magnetic 
effect, but before they are described in detail, the general use 
and method of connecting up voltmeters and ammeters will be 
considered. 



6? G Naval Electricians' Text Book 

The Use of Voltmeters and Ammeters. 

An ammeter, as its name implies, measures current, while a 
voltmeter measures voltage or difference or fall of potential. As 
constructed, most voltmeters are simply special forms of ammeters, 
though, in some cases, the opposite might be said. 

An ammeter measures directly the strength of the current flow- 
ing through its coils, and in order that the current flowing in a 
circuit may not be altered by the introduction of the instrument 
which measures it, it is evident that the ammeter should have as 
little resistance as possible. 

A voltmeter measures the difference of potential between two 
points, and it is clear that only so much of the current flowing as 
is necessary for the proper sensitiveness of the instrument should 
be diverted through the voltmeter. The voltmeter thus should 
have a very high resistance both for the sake of economy and accu- 
racy. If a high resistance is connected in series with a sensitive 
ammeter that will measure small currents, then the current passing 
would be proportional to the voltage at the terminals and the 
instrument could be made to indicate volts. 

The current flowing through an ammeter is proportional to the 
difference of potential at the terminals of the instrument, and 
from this it might appear that the difference of potential between 
two points might be measured by simply joining an ammeter be- 
tween the two points, recording the number of amperes flowing 
and from the resistance of the ammeter infer the difference of 
potential between the points. But if such a low resistance as that 
of an ammeter be connected between the two points, the total cur- 
rent between those points would be materially changed and the 
very act of connecting the ammeter would alter the difference of 
potential required. 

For instance, if an ammeter was connected to the terminals of 
a battery with no other circuit, it would not indicate the E. M. F. 
of the battery, but what could be obtained would be the fall of 
potential through the instrument. If the battery had a separate 
circuit, and it was desired to measure the fall of potential through 
that circuit, it is evident an ammeter would not be available for 
doing it by connecting it across the terminals of the battery. The 



Measuring and Testing 



677 



H# 



act of connecting the ammeter would reduce the current in the 
external circuit, and its resistance remaining unchanged, the differ- 
ence of potential would be considerably lowered. What is wanted 
is the difference of potential before the instrument is introduced 
and what might be obtained is the difference of potential after the 
instrument is connected. The less current, then, that is absorbed 
by the instrument measuring difference of potential, the more accu- 
rate it is, and it is seen that as the ammeter has more and more 
resistance it develops into a voltmeter. 

Further reasons for the peculiar construction of voltmeters and 
ammeters and the objects to be attained by them may be illus- 
trated by a simple example. 

In Fig. 307 is represented a typical 
battery circuit, consisting of a few cells, 
leading wires and a resistance R joined 
between the terminals t and t'. If the 
E. M. F. of the battery is constant, there 
will be a constant current flowing in all 
parts of this circuit, the same through 
the battery, through the connecting wires 
and through R; this current depending 
on the E. M. F. of the battery and the resistances of the several 
parts. Suppose the E. M. F. of the battery and all the resistances 
are accurately known, then the current flowing in any portion of 
the circuit will be known, and the potential may be calculated for 
any two selected points. These results can be obtained absolutely 
without the use of instruments. 

Let 

E = 12, the E. M. F. of the battery; 
r = 2 ohms, internal resistance of the battery ; 
r' = 1 ohm, resistance of leading wires ; 
R — 3 ohms, resistance between t and if ; 



^AAAA/W^— j 

Fig. 307. 



then 

C, 



law = 



the current flowing in any portion of the circuit, by Ohm's 
12 



= 2 



amperes. 



1 + 2 + 3 

By the same law, also, the difference of potential between t and 
if is 2 X 3 = 6 volts. 



678 Naval Electricians' Text Book 

Now suppose it is wished to measure these values by instru- 
ments, the question becomes, where should they be placed in circuit 
or how should they be connected in order that the values already 
known to be correct should not be materially changed. It has 
already been shown that to measure a current, the current must 
pass through the instrument, and in order that the existing current 
may not be changed, the ammeter must necessarily have a very 
low resistance and be directly connected in series with the circuit. 
If the resistance is not low but still connected in series, the current 
value would be materially changed. If the resistance is low, but 
not connected in series, but as a shunt between two points, the 
external resistance will be reduced, thus increasing the battery 
current. 

To measure the difference of potential between two points, the 
instrument must be joined as a shunt to those points, and in order 
that the current between them may not be greatly changed, the 
resistance of the voltmeter must be very great. 

The connection of the instruments for 

|_J l_| l] a measuring the battery current, and the 

I 'I j difference of potential between t and if 

is shown in Fig. 308. 

A represents the ammeter and V the 
voltmeter, A connected for measuring 
the total battery current, and V for 
measuring the difference of potential be- 
Fig 308 tween t and f. Suppose A had a resist- 

ance of .01 ohm and V a resistance of 
15,000 ohms. If V had been inserted in A's place to measure the 
current, the value of C would be 

12 
C = i + 2 + 3 + 15,000 = • 00079 am P eres - 
If A had been used to measure the difference of potential be- 
tween t and if, C would be 

12 

C = q v 01 = ^'^ am P eres > 

1 + 2 + 3+^01 
and the difference of potential between t and if would be 
3.98 X (.0099 = joint resistance between t and t') — .0394 volts. 





-A/wwv^-^ 



Measuring and Testing 679 

If A were put in V's place and V in A's, C would be 

12 

C = ,-, v n i = .00079 amperes 

l + 2 + |-^oT+15,000 

and the difference of potential between t and f would be 

.00079 X (.0099 = joint resistance) = .0000078, 
figures which do not bear any resemblance to the real values, and 
which show the effect of connecting up the instruments wrong. 
If they are connected as in the figure, C would be 
12 



3X15,000 
1 + * -r 3 _|_ 15;0 oo + - Ui 



= 1.9963 



3.9926 volts. 


1.9963 


a 


5.9889 


a 


.0199 


u 



and the difference of potential between t and f 

1.9963 X (2.9994 = joint resistance) = 5.9877, 
results which differ slightly from the values known to be correct. 
With this arrangement the fall of potential around the circuit 
would be 

Through the battery 2 X 1.9963 = 
" wires 1 X 1-9963 = 
wire t, f 3 X 1.9963 = 
A .01 X 1-9963 = 

or Total fall = 11.9977 " 

Care in Using and Connecting Voltmeters and Ammeters. — It 

has been shown by figures what the result would be by using a 
voltmeter for an ammeter or vice versa, but they do not tell the 
whole story. There ought to be no difficulty in distinguishing one 
from the other, for they are always marked. The reading of the 
scale will always be a guide, as they are marked either volts or 
amperes. 

If an ammeter were used for a voltmeter on a high potential 
circuit, on account of its low resistance and the high potential a 
very large current would be apt to flow, damaging not only the 
instrument but other parts of the circuit. If a voltmeter was used 
as an ammeter, very little current would flow, on account of the 
high resistance, unless the E. M. F. was very high, in which case 
the delicate coils of the voltmeter might be burnt out. 



680 Naval Electricians' Text Book 

Ordinarily it does not injure voltmeters or ammeters to connect 
them np wrong as far as polarity goes, the pointer simply indi- 
cating in the wrong direction. Too much current sent suddenly 
through an instrument may throw the pointer violently against its 
upper stop, rendering it liable to be bent. More current than is 
designed for may cause the coils to heat to a dangerous degree, burn- 
ing or destroying the insulation of the conductors. 

In making connections with a voltmeter or ammeter, it is better 
to make the connections on the instruments first, and to the circuit 
last, and still better to have a switch in the circuit, so all connec- 
tions may be made without danger of injuring the terminals by the 
arc which might otherwise be formed. 

Instruments should be used with care and judgment at all times. 
The best ones are made with great care with small pivots and jewel 
bearings, and rough handling is apt to dull the points or crack the 
jewels. Eough handling is also liable to weaken the permanent 
magnet in instruments like those of the Weston type which will 
cause incorrect readings. 

Instruments should not be placed close to a running generator 
or motor, on account of the danger of having the magnetic fields 
distorted by the stronger fields, nor should instruments with per- 
manent magnets be placed close to one another, not within 2 to 3 
feet. 

Weston Voltmeters. 

The general form invariably used in the service on shipboard is 
that of the Weston type, being a development of the early d'Arson- 
val galvanometers. Two forms are usually supplied, one the station 
type for use on permanent switchboards, and the other a portable 
instrument for measurements about generators, motors, or measure- 
ments for resistance or fall of potential in different parts of a 
circuit. They are constructed on the same principle, already quoted 
under the second class of instruments given under the heading 
magnetic effect. 

The permanent magnetic field is produced by a permanent steel 
magnet of peculiar form, half circular, half horse-shoe (see Fig. 
310) ; the outside form of the face of the portable instrument 



Measuring axd Testixg 



681 



being in general the shape of the magnet. The form of the pole 
pieces is also peculiar and is such that the deflecting coil moves in 
a constantly uniform field, and this is necessary in order to have 
the deflections follow the proportional law. Between the poles of 
the magnet is pivoted on very sharp points resting on jeweled bear- 
ings, a very fine light rectangular coil of wire, as shown in Fig. 
309. The motion of this coil is restrained by two fine spiral 
springs, each something like the hair spring of a watch, one at the 
top and one at the bottom, through which the current is led into 
and out of the instrument through the pivoted coil. 

The index that registers the 
reading on the face is a long 
thin aluminum pointer *and is 
secured to the top of the coil, 
moving with the coil as it is 
deflected. When no current is 
flowing, the action of the 
springs keeps the coil in its 
zero position, the pointer then 
registering zero in the scale. 

Within the movable coil is a 
central cylindrical core of soft 
iron, this tending to strengthen 
the magnetic field of the per- 
manent magnet, or rather tend- 
ing to reduce the resistance of the permanent magnetic circuit. 
The movable coil is wound on a light copper frame, which in addi- 
tion to serving as a support for the coil acts as a magnetic brake, 
moving as it does in an intense magnetic field and having currents 
induced in it opposing its motion. This makes the instrument 
practically " dead beat." As soon as current flows, the pointer at 
once takes a position to indicate the voltage and there is no 
" hunting " or fluctuating of the pointer. 

The movable coil has a resistance of about 60 ohms and a full 
deflection is produced when a difference of potential of about .6 
volt is applied to the coil. When measuring higher voltages than 
this it is necessary to insert resistances in series with the coil, 




Fig. 309.— Coil and Poles of Weston 
Instruments. 



682 Naval Electricians' Text Book 

the added resistance being proportional to the maximum difference 
of potential to be measured. The inserted resistance must be calcu- 

fiO 
lated for a resistance of -— = 100 ohms for each scale division. To 

.0 

measure 100 volts would require a resistance of — X 100 = 10,000 

ohms. This resistance is usually a coil of platinoid or manganin 
wire placed inside the instrument case, and as this alloy has a very 
low temperature coefficient, the temperature error is inappreciable 
and the instrument can be left continuously in circuit ; the loss of 
power owing to the high resistance being very small. 

When this voltmeter is connected to the two points of different 
potential, there is a temporary magnetic field set up around the 
movable coil, and the coil experiences a pull on one side and a push 
on the other tending to make it rotate, and it takes a position 
dependent on the resultant of the forces due to the two magnetic 
fields and the tension of the springs. The same current always 
produces the same field and the same deflection, so by proper cali- 
bration or comparison with other standards, the proper number of 
volts may be marked off on the scale. 

As the coil moves practically in a uniform field, the subdivisions 
on the scale are very nearly equal. 

The portable voltmeters are usually calibrated for and marked 
with two scales, one for high reading, and the other for low read- 
ing. The low-reading scale is made available and effective by 
placing properly wound resistance coils in series with the movable 
coil, this arrangement necessitating a third terminal on the 
instrument. 

Weston Ammeters. 

The ammeters furnished for ships' use are generally of the 
Weston type (see Fig. 310), and their governing principle and 
construction is exactly similar to that of the Weston voltmeter, 
the scale being marked to register amperes in place of volts. In 
some of the earlier forms it was usual to lead the whole current to 
be measured to and through the ammeter, in the inside of which 
was a resistance slightly greater than that of the leading wires, 
and the current that flowed through the ammeter coils was taken as 



Measuring axd Testing 683 

a shunt from the ends of this resistance. Only a portion of the 
main current flowed through the instrument coils, which acted in 
all respects exactly as a voltmeter measuring the difference of 
potential between the points to which it was connected. 




Fig. 310. — Weston Portable Ammeter. 

Ampere Shunt. 

In order to obviate the necessity of leading the heavy wires to 
the instrument on the panel board, a later practice is to insert 
the resistance that was formerly placed in the instrument directly 
in the leads in some convenient place on the switchboard. Such a 
resistance is called the ampere shunt, and it consists of a resistance 
slightly greater in value than the main conductors in which it is 
inserted. A general form of this resistance is shown in Fig. 311. 

Two copper terminals, a, a, are soldered to the ends of the main 
conductor ~b, b. Between these copper terminals are strips of metal 
alloy c, soldered in place to the terminals: the resistance being in 
strips to better allow for ventilation. The leads to the ammeter 
terminals d, d, are brought to the copper terminals and clamped 
at e, e. 

On account of the slight increase in resistance of the metal strips 
over the rest of the conductor, a small proportional part of the 



684 



]\ t aval Electricians' Text Book 



current is shunted through the ammeter, which thus practically 
measures the difference of potential between the ends of the resist- 
ance, but this, being proportional to the main current flowing, by 
proper calibration measures the whole current. 

It is very necessary that the shunt should have a practically 
constant resistance as it may carry constantly varying currents 
and this is effected by using an alloy of low temperature coefficient, 
such as platinoid or manganin. 

It must be remembered that the ammeter is calibrated with a 
certain resistance in the leading wires from the terminals of the 
resistance to the instrument, and the resistance of these wires must 




3 



5=- 



Fig. 311. — Ampere Shunt. 



not in any way be changed by splicing or cutting, for the main 
resistance remaining constant, it is evident that the resistance of 
the leading wires must also remain constant if the instrument is 
to correctly record. 

There must be perfect electrical connection between the shunt 
and the main conductor and between the shunt and the ammeter 
leads. Any resistance due to a bad contact in the former case 
would cause the ammeter to read too high and in the latter case 
too low. 

The coil of the instrument is the same for all ranges and the full 
deflection of the needle is obtained when the difference of potential 
at the terminals is .06 volt. The resistance of the shunt is such 
that this difference of potential, about .06 volt, exists when the 



Measuring axd Testing 685 

shunt is carrying the maximum current and the resistance of the 
shunt is varied by changing the number of strips of alloy in it, 
their lengths remaining the same. 

The Testing Set. 

The testing set for measuring and comparing resistances ordi- 
narily consists of a battery of a few cells, a galvanometer, and a 
combination of resistance coils of known value. The principle of 
all resistance testing sets is that of the Wheatstone bridge. 

Before explaining the principle of the Wheatstone bridge it will 
be first necessary to explain the action of the galvanometer, as this 
instrument has been mentioned in several preceding tests, and will 
find constant reference in the future. 

The Galvanometer. — This is an instrument for indicating and 
comparing currents, not to measure them, except in an indirect way. 
One of the most delicate instruments for showing the effect of an 
electric current is an ordinary magnetic compass needle. It will be 
remembered that the definition of the ampere was based on the 
effect a current of electricity produced on a magnetic pole. It 
will be well here to repeat the definition as finally determined on. 
If a conductor one unit in length (one centimetre) be bent into an 
arc of a circle one unit in radius (one centimetre) and a unit 
magnetic pole be placed at the center, then the current through 
such a conductor will be one unit of current if it acts on the unit 
magnetic pole with a force of one dyne. The effect of the current 
is inversely proportional to the square of the distance, r the radius, 
from the magnetic pole. Evidently there could be no closed cir- 
cuit in such a conductor, and to make one complete turn around 
the pole, there would have to be a conductor in length equal to 2irr. 
The force then in dynes which a current C would exert on a unit 
pole due to one complete turn would be expressed by the equation 

2-rC 

~^r~ =f, and if the coil consisted of n complete turns, would be 

%*nC 

r ~ *' 

If such a coil surrounds a magnetic needle, each unit of strength 
of the needle will be acted on by a force of / dynes. The needle 



686 



Naval Electricians' Text Book 



is held in the magnetic meridian by the horizontal force of the 
earth's magnetism, this force designated by H acting on each unit 
of strength of the magnet. If the needle is acted upon simul- 
taneously by these two forces it will take a position at an angle 8 
from the meridian that will represent the re- 
sultant of the direction of the two forces. If 
the coil is in the meridian, the force due to 
the current acts at right angles to it, and the 
force due to the earth acts in the meridian. 
Fig. 312 represents the forces acting on the 
needle, NS being the meridian, 8 the angle of 
deflection, H the horizontal force of the earth 
tending to hold the needle in the meridian and 
/ the force due to the current flowing in a coil 
in the meridian over the needle. It is evident, 
then, that 




Fig. 312. 

Forces Acting on 

Needle in Tangent 

Galvanometer. 



/ = B"tan8, 



or 



2xnC 



= H tan 8. 



These quantities all being known, it follows that C in CG8 units 
= ^— H tan 8, or C is proportional to tan 8. This is the principle 
of the tangent galvanometer. 



The Wheatstone Bridge. 

The Theoretical Bridge. — The bridge (Fig. 313) consists of four 
arms 1-2, 2-3, 3-4 and 4-1, in three of which are variable coils of 
known resistance, and in the fourth, the unknown resistance X is 
placed. A battery B of a few cells is connected to 1 and 3, and a 
galvanometer G is connected to 2 and 4. 

Let A,B, C and X represent the four resistances and C a , C& , C c 
and C x the currents in those resistances at any time. 

A and B usually contain coils of resistance varying by multiples 
of 10, as 1, 10 and 100, and 10, 100 and 1000, and they are called 
the balance arms. The arm C contains numerous coils of resist- 
ance of such values that any whole integer may be made, and this 
is called the rheostat arm. 



Measuring and Testing 



687 



The current from the battery divides at 1, flows through A 
and C, B and X to 3 and thence back to the battery. When there 
is a difference of potential between 2 and 4, current will also flow 
in that branch, either towards 2 or towards 4, depending on the 
relative resistances of A and B. If current does flow through the 
galvanometer, it will be shown by the needle being deflected, but if 
there is no difference of potential between 2 and 4, no current will 
flow in that branch and the needle will remain at rest. When this 
happens a balance is said to be established between the four arms, 
and as this condition always exists in making a measurement, it is 




Fig. 313. — Connections of Theoretical Wheatstone Bridge. 



called a null method. There are keys in the battery circuit and in 
the galvanometer circuit, so current only flows when making a test. 
When current is flowing, there is a certain absolute potential 
at 1 and a lower potential at 3 in order that current should flow in 
that direction; and there is also a certain potential at 2 and a cer- 
tain potential at 4. In order that there may be no difference of 
potential between 2 and 4, the fall of potential from 1 to 2 must 
equal the fall in potential from 1 to 4, although the currents and 
resistances in these branches may be different. Similarly the fall 
in potential from 2 to 3 must be the same as from 4 to 3. In 
other words, by Ohm's law 

C a A = C h B and C C C — C X X. 



688 Naval Electricians' Text Book 

When there is no difference of potential between 2 and 4 the 
current in A is the same as in C; and in B the same as in X, or 

C a = C c and C h = C x . 
Therefore 

C a A = C h B and C a C = C h X 
and dividing one by the other 

A B v BC 

from whence A, B and C being known, X is readily calculated. 
If the resistances in the balance arms A and B are equal when 
a balance is obtained, then the unknown resistance X is equal to 
the resistance found in C. If B is greater than A, the resistance 
in C must be multiplied by the number of times B is greater than A, 
and similarly if smaller than A, divided by the number of times 
it is smaller. 

Resistance Coils. — The resistance coils are usually made of Ger- 
man silver wire as that is effected very little in its resistance by a 
change of temperature. In order to prevent the effects 
of self-induction due to the current and of magneto 
electric induction due to magnets or soft iron in the 
neighborhood of the coils, it is necessary that the cur- 
rent be doubled back on itself. The wire should be 
either wound on the bight as in Fig. 314, or, if there 
are to be many turns, the first layer should be wound 
right handed and the next left handed and so on, each 
layer being secured so as not to unwind when the next 
Fig. 314. ! ave r is wound. Then again the bobbin on which the 
.p . wire is wound may be divided into halves, the upper 

Coils. na ^ being wound right handed and the lower left 

handed. 
After the coils are wound they are dipped into melted paraffin, 
so on cooling every portion is covered, being protected mechanically 
and electrically. 

The rheostat arm of the bridge may be used as a separate resist- 
ance, and if so used, care must be taken that too great current is 
not sent through coils, as they are delicate and liable to be burnt 




Measuring axd Testing 689 

out. The same precaution is necessary in using the galvanometer 
as a separate instrument, as the coils of that instrument cannot 
stand too heavy a current. 

Silver Chloride Cell. — As has been stated this form of cell is 
ordinarily used in testing sets, and in order to use the set intelli- 
gently a short description of it is given. The positive electrode is 
a zinc rod and the negative electrode consists of a silver rod sur- 
rounded by silver chloride melted into a cylinder upon the rod. 
The electrolyte is sal ammoniac, but in the dry cell, as used with 
testing sets, the water is replaced by some gelatinous substance 
which differs in its composition according to the maker, it generally 
being a paste containing zinc oxide, zinc chloride, sal ammoniac, 
lime and water. 

When the cell generates current the chlorine in the ammonium 
chloride (sal ammoniac) is displaced by the zinc and the ammo- 
nium set free displaces the chlorine in the silver chloride, leaving 
metallic silver deposited on the silver electrode. There will be no 
free gas given off unless the cell is worked too hard. This cell 
gives under ordinary conditions about 1.1 volts. 

Galvanometer. — The form of galvanometer used with most test- 
ing sets consists of many turns of fine silk-covered wire wound on 
a single bobbin. The needle is pivoted and lies exactly in the center 
of the coil and is entirely covered by it. The needle carries a 
pointer at right angles to it and passes over a scale on which divi- 
sions are marked. The needle is provided with a lever for lifting 
it clear of its pivot when not in use, and is controlled by a separate 
magnet to enable it to be used in any position, the pointer showing 
zero on the scale when no current is flowing. 

These galvanometers are made to be very sensitive, a current of 
one-twentieth of an ampere giving a deflection of 25 degrees. This 
is effected by the great length of wire used on the bobbin, the near- 
ness of the wire to the needle and the delicate pivoting of the 
needle. «•* 

Service Testing Set. 

One form of Wheatstone bridge furnished to ships is that made 
by Queen & Co., called the Queen-Acme Portable Testing Set. 



GOO 



Naval Electricians' Text Book 



The bridge, battery and galvanometer are all placed in a compact 
box of seasoned mahogany fitted with lock and key. 

The upper face of the set is shown in Fig. 315, the full lines and 
circles showing the connections, binding posts, keys and terminals 
on the outside of the box and the dotted and broken lines the con- 
nections under the face which is of hard rubber. 

The Coils. — The coils are wound of platinoid wire carefully 
seasoned to prevent gradual changing of the resistance with time. 
The wire has a low temperature coefficient and the endeavor is to 
have corresponding coefficients for all the coils. The rheostat coils 
are adjusted to an accuracy of J of one per cent and the bridge coils 




IQOC1XM3CX30! 




UO 



(G»j^ -(^Vtnrwy^) 



* 3 (O) 



Fig. 315. — Queen-Acme Testing Set. 



to an accuracy of ■£$ of one per cent. The rheostat coils are sixteen 
in number, their combined resistance being 11,110 ohms. In each 
bridge arm there are three coils of 1, 10, 100 ohms and 10, 100, 
1000 ohms respectively. The commutator admits of a ratio of 1 
to 1000 on either bridge arm, and the theoretical range is from 
.001 to 11,110,000 ohms, though for resistances above 1,000,000 
ohms additional battery power is required. 

The Galvanometer. — This of the d'Arsonval type. The current 
from the battery flows in a conductor wound around an iron core 
on which the needle is pivoted, and this coil and core revolves be- 
tween the poles of a permanent magnet which produces an intense 
permanent magnetic field. When current flows around the coil 
another magnetic field is set up, and the coil carrying the needle 



Measuring and Testing 691 

takes a position due to the resultant forces of the permanent and 
the temporary fields. 

The Battery. — This consists of four special dry cells, one or more 
of which may be used as desired. They maintain a steady E. M. F. 
and are good until exhausted. The cells have a very low resistance 
and will last for months with care even though the set may have 
daily use. 

The Keys. — There are two single contact keys. The left-hand 
key is a single contact key in the battery circuit. The right-hand 
one is in the galvanometer circuit and is a short-circuit key. When 
depressed it closes the galvanometer circuit and when released it 
short circuits the galvanometer, bringing it immediately to rest. 

Connections and Circuits. — The connection and circuits are 
readily understood by referring to Fig. 315. The top row of blocks 
is connected to the bottom row by a heavy copper bar joining the 
right-hand blocks. These two rows together constitute the rheostat. 
Any resistance from 1 to 11,110 ohms may be obtained in this 
rheostat by removing the proper plugs. The lower left-hand block 
of the rheostat is connected to the lower line post D. The upper 
line post C is connected to block X. This block X has no other 
permanent connection excepting that it is joined to one end of the 
galvanometer key. The block R is connected to the upper left- 
hand block of the rheostat and otherwise has no connection except- 
ing by plugs. The end blocks of the middle row are connected 
by a heavy copper bar. Each half of this row constitutes a bridge 
arm, designated A and B respectively. Starting from the lower 
line post D, the circuit is continuous from there through the 
rheostat and then through first one bridge arm and then the other 
back to the other line post C. 

The function of the commutator is to transpose the two bridge 
arms A and B so that they are passed through in reverse order. 
All of the above connections are in circuit with the resistance 
being measured and are made sufficiently heavy to add no appre- 
ciable resistance to the circuit. 

The two battery terminals + and — are connected, one directly 
to the common junction of the two bridge arms, the other through 
the battery key to the rheostat. 



692 Naval Electricians' Text Book 

The two galvanometer terminals are connected, one directly to 
the block R, while the other connects through the galvanometer 
key to the block Z. The blocks A, B, R and Z are joined by 
plugs as shown by the shaded circles between the blocks. 

The Commutator. — This consists of the blocks A, B, R and Z 
and two plugs. When these two plugs are in the position shown 
in the figure, the bridge arm A is connected to the rheostat and 
the bridge arm B to the line. In this position the following rela- 
tion holds 

A__ R^ 
B ~ X 
and the bridge is in a position for measuring high resistances, indi- 
cated by the arrow marked H. 

If the plugs have the opposite position, the bridge arms are re- 
versed, the one that was connected to the rheostat now being con- 
nected to the line, and the one to the line being joined to the 
rheostat. In this position, the following relation holds 

B ~ R 

and the bridge is in a position for measuring low resistances, indi- 
cated by the arrow marked L. 

Uses of the Set. — This testing set may be used to measure resist- 
ances, either high or low, insulation resistance, to compare E. M. F. 
of batteries, to check a voltmeter, to measure battery resistances, to 
check an ammeter and to make what is known as the Varley Loop 
Test. These will be described in Chapter XXX. 

Magneto. 

This is an instrument used in testing electrical circuits and in 
a limited degree for measuring resistances. It can be used to 
detect an open circuit, to detect a ground or to locate a fault in an 
open circuit, and within limits to measure resistance. 

In its most common form, it consists of two parts, a small 
dynamo or generator and a bell. The connections are shown in 
Fig. 316. 

The field of the generator is furnished by two or more perma- 
nent steel magnets. Between the poles is rotated a small closed 



Measuring and Testing 



693 



armature, usually a simple rectangular coil wound on an iron core. 
There is a small crank on the outside of the case containing the 
generator to which is attached a toothed wheel which engages a 
smaller wheel connected directly on the armature shaft, so one 
revolution of the crank gives a great many to the armature. Con- 
nected in series with the armature is the bell circuit, and when con- 
nected for testing an outside circuit, that circuit is also in series 
with the armature and bell circuit. Current from the armature 
is led around an electromagnet, between the legs of which and on 
the end opposite the yoke, is pivoted an iron armature. This arma- 
ture has secured to it at right angles an arm terminating in a 
striker for the bell. This striker projects through the case, and has 
motion between two bells, striking them alternately as it vibrates. 



C^t<0± 



II 



u 



=L 



Fig. 316.— Magneto. 



When the armature is revolved and the armature turned in the 
ield of the permanent magnets, alternating currents are induced 
n the armature circuit and this being in series with the electro- 
nagnet causes alternating currents which cause an alternating 
change of polarity, causing the armature to be attracted first to 
me leg and then the other. This causes the striker to vibrate and 
i ringing of the bell is the result. This can only happen, how- 
ever, when the armature circuit is complete through some outside 
:ircuit. 

The E. IE. F. produced in the armature depends to a great extent 
>n the speed with which it is turned, but a good magneto should 
levelop from 50 to 100 volts. For certain purposes, as will be 
llustrated later, it is necessary to know the maximum resistances 
hat current can be forced through, and these data are usually 
tamped on them, varying from 3000 to 30,000 ohms. 



694 



Naval Electricians' Text Book 



Ohmmeter. 

This instrument as its name signifies is one for measuring re- 
sistance, the value of the measured quantity being read directly in 
ohms from the scale of the instrument. In testing for faults or 
testing the goodness of the insulation used in an electric light in- 
stallation, it is necessary that an E. M. F. at least as great as that 
under which the plant is to work, should be used. Such a high 
E. M. F. would be too great for use with the ordinary Wheatstone 
bridge testing set, so the ohmmeter is designed to be used with a 
small magneto giving the desired E. M. F., when the resistance can 
be read directly from the instrument. This instrument is of par- 
ticular value in measuring insulation 
resistance, affording the most ready 
and rapid means of measuring it, its 
practical application being shown later. 
Fig. 317 shows the general outside 
appearance of an ordinary ohmmeter. 
The two right-hand terminals are for 
the leading wires from the source of 
supply (generally a small magneto ma- 
chine). They are marked -f" and — . 
The two left-hand terminals are for the 
leading wires to the unknown resist- 
ance to be measured. There are two contacts in the middle marked 
A and B, corresponding to the two scales on the face. If the switch 
is on A, the outer scale is to be used, and if on B, the inner scale. 
Fig v 318 shows the interior construction, being a half section 
through the coils viewed from underneath. There are three coils, 
the two outer ones, a, a, being placed with their planes parallel and 
the coils connected in series; the third, b, being placed between 
them with its plane and magnetic axis at right angles to those of 
a, a. There is a small steel needle pivoted in the center of the 
coil b with its magnetic axis lying in the common axis of a, a. To 
this needle is attached the pointer and the coil b is so cut away 
as to allow a wide range for the travel of the pointer. Underneath 
the pivoted needle is a small weak bar magnet to counteract the 
earth's magnetism, so the needle only acts under the influence of 
the coils when current flows through them. 




Fig. 317.— Ohmmeter. 



Measuring axd Testixg 



695 



Any current flowing through a, a, tends to keep the needle in its 
zero position with its length in the common axis of a, a. In this 
position the needle is parallel to the plane of b and any current 
through b tends to deflect it, and the needle will take a position 
depending on the relative strength of the current in the coils. 

The coils a, a, of high resistance are connected only to the source 
of E. M. E., but the coil b which is connected to the same source 
of E. M. E. is also connected in series to the high resistance to be 
measured. The current through the deflecting coil b is inversely 
proportional to the resistance and directly proportional to the 
E. M. F., while the current 
through the magnetizing coils 
a, a, is directly proportional to the 
same E. M. F. Any variation of 
the E. M. F. affects equally both 
the magnetizing and deflecting 
currents, so the deflection of the 
needle is simply inversely propor- 
tional to the resistance to be meas- 
ured, the resistance of b being 
small. 

If the resistance to be meas- 
ured is infinite no current flows 
through b and there is no deflec- 
tion of the needle. As soon as the resistance is at all lowered a 
certain small current flows producing a small deflection, and by 
simple calibration the scale can be marked to indicate directly in 
ohms the value of the unknown resistance. 




Coils of Ohmmeter. 



The Evershed Testing Set. 

The ohmmeter described in the preceding section is known as 
the Evershed ohmmeter, but a later form of this instrument is 
now made, known as the Evershed Testing Set. This instrument 
is made by Queen & Co., and the description and use of this instru- 
ment has been furnished by the makers. 

The electrical principle involved is the same as in the case of 
the ohmmeter, but the arrangement of the coils is slightly differ- 



696 



Naval Electricians' Text Book 



ent. This is shown in Fig. 319. The leads from the magneto are 
secured to the terminals marked A ( + ), B ( — ), and the unknown 
resistance to terminals C and D, one of which is marked " Earth " 
and the other " Line/' Eor testing insulation the conductor under 
test is connected to the earth terminal, and the other terminal is 
grounded. 

Inside the terminals A and B, the current divides, part flowing 
through the coil P, called the pressure coil, through a constant 
resistance R, and part through the unknown resistance and through 




Fig. 319. — Connections of Evershed Testing Set. 



the coils MM in series, these coils being known as the current 
coils. The action of the pressure coil is to keep the axis of the 
needle NS perpendicular to its own coil and that of the current 
coils to deflect the needle. This needle carries the pointer travel- 
ling over a graduated scale from points marked to infinity. 

When there is no leakage on the line, there is no current through 
MM and consequently the needle remains at rest, with the pointer 
indicating infinity, showing an infinite resistance on the line. 
When the line resistance is so low as to be negligible, the current 
flowing through the current coils depends on the voltage and the 



Measuring axd Testixg 697 

resistance of the coils, and the needle will be deflected to a position 
in which the turning moments of the two coils P and MM are 
balanced. This point on the scale is marked and for any given 
resistance in the line the pointer will come to rest at a point be- 
tween and infinity. The position of the pointer will not be 
changed by altering the voltage of the magneto, for the currents in 
the coils will be increased or decreased together, so their ratio 
remains unchanged. 

The scale is marked in tenths and units of megohms, thus indi- 
cating directly the resistance measured. 

Magneto. — In the latest pattern of this testing set, the magneto 
is built after the fashion of a modern continuous-current generator. 
It has a tunnel-wound armature with a finely laminated core built 
from stampings of best iron of " transformer " quality, a special 
form of commutator with elastic roller brushes and roller bearings 
for the armature axle. The armature is driven by double gearing 
by a winch handle so hinged that it may be turned into a recess 
in the box when not in use. A flexible double conductor connects 
the magneto to the ohmmeter. 

Needle. — The ohmmeter has a very finely pivoted astatic needle 
system, magnetized by the magneto current. The needle system is 
automatically lifted off the jewel bearing and clamped by the action 
of shutting the lid of the box. The current coils MM are wound 
with an enormous number of turns of the finest wire so as to secure 
the maximum sensibility. A one-ninth shunt 8 is provided so as 
to reduce the sensibility ten times when low insulation resistances 
are being tested. 

Instructions for Use. — Adjust the ohmmeter until the bubble is 
in the center of the spirit level. 

Place the generator not less -than 18 inches away from the ohm- 
meter and couple its terminals to the marked terminals on the 
ohmmeter. 

Couple the mains to be tested to the line and earth terminals of 
the ohmmeter. Turn the generator handle steadily in either direc- 
tion at any speed above 60 revolutions per minute and the ohm- 
meter index will point to the resistance under test. 



CHAPTEK XXX. 

MEASUREMENTS. 

The measurements to be given are only those that can be made 
with the instruments described in the preceding chapter, viz.: the 
voltmeter, ammeter, testing set, magneto and ohmmeter. In addi- 
tion to the above, a few standard resistances may be necessary, but 
they can usually be found on board ship, as, for instance, the 
rheostat arm of the testing set when small currents are used, or 
the " ampere shunt " resistance used with the ammeter when large 
currents are used. 



To Measure Current. 

Current is measured by connecting an ammeter directly in the 
circuit through which the current is passing. 

To Measure Current without Opening the Circuit. — This can be 
done where there is a convenient switch in the line, for the ammeter 
may be connected around the switch, and the switch then opened, 
when the full current will pass through the ammeter. 

To Measure Current by Resistance and Voltmeter. 

By Ohm's law the fall of potential through a conductor equals 
the product of its resistance and the current then flowing. By 
knowing the resistance and measuring the difference of potential 

between its ends, the cur- 
rent is at once obtained. 
Fig. 320 shows how the 
connection should be 
made. 

R is the standard resist- 
ance and V the voltmeter, 
which in this case should 
be a low-reading one. 




-D 



O 



Fig. 320. — Connections for Measuring 

Current with Resistance 

and Voltmeter. 



Measurements 



699 



To Measure E. M. F. 

E. M. F. is measured by connecting a voltmeter to the two points 
between which, the difference of potential is required. 

To Measure Resistances. 

High resistance may be measured by a voltmeter, by the testing 
set or by an ohmmeter. 

Low resistance may be measured by an ammeter and voltmeter, 
or by a voltmeter and standard resistance. 

To Measure Resistance with Voltmeter. — To do this requires a. 
voltmeter of known resistance and a source of constant potential, 
as a running generator. The difference of potential across the 
mains of the generator is first measured and then the resistance to 
be measured is connected in series with the voltmeter, and the fall 
of potential through these two is 
measured across the mains whose 
difference of potential is constant. 
This is represented in Fig. 321. 

Suppose V is the reading of the 
voltmeter when connected di- 
rectly across the mains and V 
the reading when it is connected 
up with R, the unknown resist- 
ance in series with it. Let X be 
the resistance of the voltmeter 
and C the current through V and 
R, then by Ohm's law V = C (X + B) 

Subtracting one from the other, 



4- 

© © 




Fig. 321. — Connections for Measur- 
ing Resistance with Voltmeter. 



md V — Y' = CR. 



Y' = CXotC = ^-, 



also 



C = 



R = 



r — v 

R ' 
(V—V) xx 
V 



all of which quantities are known. 

This method is available for high resistances and is particularly 
adapted for measuring insulation resistance as described farther on. 



700 Naval Electricians' Text Book 

To Measure Resistance of. a Voltmeter. — This is just the con- 
verse of the above, -requiring a source of constant potential and a 
high resistance. The connections and readings are made as before, 
when the resistance of the voltmeter would be equal to the other 
resistance multiplied by the second reading and divided by the dif- 
ference of the readings. 

The resistance of most voltmeters is marked on the box or case, 
but the above would be available in case it was unknown. 

With a Weston 150-volt range voltmeter satisfactory resistances 
can be measured from 100 to 2500 ohms, the most accurate being 
for resistances about equal to that of the voltmeter. With the low- 
reading voltmeter, from to 5 volts, a range from 3 to 85,000 ohms 
may be measured. 



© 



rvwwv 



Fig. 322. — Connections for Measuring Resistance with Voltmeter and 

Ammeter. 

To Measure Resistance with an Ammeter and a Voltmeter. — To 

do this it is only necessary to connect up the resistance in series 
with the ammeter and connect a voltmeter at the terminals of the 
resistance. Then, by Ohm's law, the resistance is at once calculated. 

From above R = -^-(Fig. 322). 

Precautions when Measuring Resistance with Ammeter and 
Voltmeter. — See that the instruments are far enough apart so that 
neither will be effected by the other, and use no more current than 
is suitable for the resistance. See that all connections are good, and 
especially those of the voltmeter. It is better to connect the am- 
meter outside the voltmeter, for the error will be less if the 
ammeter measures the slight current through the voltmeter than 
if it were connected so that the voltmeter recorded in addition the 
fall of potential through the ammeter. 



Measurements 



701 



To Measure Resistance with a Voltmeter and Standard Resist- 
ance. — The circuit whose resistance is to be measured is connected 
in series with the standard resistance and a steady current sent 
through both. The voltmeter is connected around the standard 
resistance and then around the unknown resistance. The current 
being the same through both resistances, the differences of potential 
are directly proportional to the resistances. A typical connection 
is shown in Fig. 323 for measuring the resistance of an armature. 

A few cells are connected up in series with the standard resist- 
ance and the armature whose resistance is to be determined. A 
voltmeter is connected to the terminals of the resistance and when 



•H 



3J 



"—& 



o 



[0 

N3J 



Fig. 323. — Connections for Measuring Resistance with Voltmeter and 
Standard Resistance. 



current is established through the circuit, the fall of potential 
through the resistance is noted. When the same current is flow- 
ing, the voltmeter is connected to the brushes of the armature or 
to two opposite segments of the commutator, and the fall of poten- 
tial noted. Calling R and D the resistances and V and V the 
readings of the voltmeter, then the current C through R and D is, 
by Ohm's law, 



C 



or D 



V'R 

IT* 



V _V 
R~ D 

whence D is readily calculated. 

In this measurement, the standard resistance should be capable 
of carrying considerable current without heating, and the " ampere 
shunt" resistance can be used to advantage. The current should 
be steady, and the resistance of the voltmeter high, and the volt- 
meter itself low reading. 



702 Naval Electricians' Text Book 

Standard Resistances. — If no resistances are available, the}' can 
readily be made on board ship. Knowing the resistance required, 
and its diameter and specific resistance, its length can be deter- 
mined as given under the subject Resistance. Its calculated resist- 
ance should be checked by actual measurement by some of the 
methods given. 

Calibration of Instruments. 

Calibration is the process of determining the value of the cur- 
rent or voltage required to move the indicator to any or all parts 
of the scale. This may be done when making a new scale or in 
checking an instrument that has been in use. For example, sup- 
pose that an instrument has a resistance of 10,000 ohms, and that 
.001 ampere causes the pointer to move an inch from its zero point. 
By Ohm's law E = C X R or E = .001 X 10,000 = 10 volts, 
so that point on the scale one inch from the starting point might 
be marked either 10 volts or .001 (one milliampere). When this 
instrument is connected between two points and current flows 
through it so that the pointer takes this position, it is then known 
that a current of .001 ampere is flowing through it, or that the 
difference of potential between the points is 10 volts. In a similar 
way the value of any other point on the scale may be determined. 

All voltmeters and ammeters should be calibrated from time to 
time by comparison with some standard instruments. To be accu- 
rate they should be compared with absolute standards, but as they 
are not available on shipboard, it is usual to compare all instru- 
ments with some standard, which in turn might be calibrated on 
shore by reference to absolute standards. 

Calibration of Ammeters. — To compare an ammeter with a stand- 
ard they are connected in series and the same current is sent 
through both, the deflection of the needle of the standard being 
noted and that of the other being compared with it. If the instru- 
ment has not changed the readings should be the same. 

The instruments should be placed far enough apart so that the 
magnetic field of one does not affect the other, and the instruments 
should be in the same relative position, that is, both level if the 
standard is correct in that position, or both vertical, as the case 
may be. 



Measurements 



703 



If a standard ammeter is not at hand, a standard resistance 
and a millivoltmeter may be used, and the current flowing through 
the resistance calculated, and this should be the value indicated on 
the ammeter under test. The connections are shown in Fig. 324. 



o 



Fig. 324. — Connections for Calibrating Ammeters. 



The instruments should be compared with increasing and then 
decreasing currents to check against errors of hysteresis and to see 
how far the instrument is affected by friction. 

Calibration of Voltmeters. — Voltmeters are compared with a 
standard voltmeter by connecting all in multiple, so that all are 
subjected to the same voltage. The voltage is then changed to 
different values and the reading of the voltmeters is compared with 
the standard. 

To Obtain Different Voltages. — In order that voltmeters can be 
compared throughout the range of the instrument, some means 
must be adopted of varying the voltages. A good method of doing 
this is to connect across the mains of a constant potential circuit, 
such as the lighting mains on ship, a piece of wire that will allow 
a small current to pass. A conductor of German silver wire is 
especially adapted for this, as its resistance per unit of length is 
uniform, so the fall of potential will be uniform. 

By connecting the voltmeters in mul- * 
tiple along this wire any difference of po- 
tential may be obtained, and comparisons 
with the standard made. It is well to 
have one common terminal secured to one 
of the mains, and another common ter- 
minal may be moved along the wire. 
The connections are made in Fig. 325. 

A and B represent the mains and R 
the German silver resistance, V the 
standard voltmeter and V the one under 
comparison. 




A 

Fig 



325. — Connections for 
Calibrating Voltmeters. 



704 Naval Electricians' Text Book 

To Connect Voltmeters to Increase their Range. — It may happen 
that a voltage is desired to be measured that is beyond the range of 
the voltmeter at hand. The range of the voltmeter may be doubled 
by placing it in series with an equal resistance. If the voltmeter 
reading to 150 volts has a resistance of 15,000 ohms, it will read 
to 300 volts when it is connected in series with an added resistance 
of 15,000 ohms or another voltmeter of the same resistance. This 
results from the fact that if the resistance of the circuit is doubled, 
twice as much pressure is required to send the same current through. 
If these two voltmeters are connected between two points whose 
difference of potential is 300 volts, each instrument will register 
150 volts, the fall of potential through each being 150 volts. The 
total fall of potential will be the sum of the fall of potential 
through each instrument. 

To Connect Voltmeters to Decrease their Range.- — Most portable 
voltmeters are provided with two resistances, by means of which 
two scale readings are available, one for high and one for low differ- 
ences of potential, and separate terminals are provided for putting 
these resistances in the circuit. It frequently happens that a high- 
range voltmeter is the only means at hand for measuring voltages, 
and a small difference of potential may be wished to be measured. 
Weston voltmeters are marked in single volts, but frequently they 
are not accurate within the first few divisions on the scale of the 
high-reading instruments. In this case it is better to connect the 
points between which the E. M. F. is required in series with the volt- 
meter and connect them both across high potential mains. 

Suppose it was required to measure the E. M. F. of a battery 
with a voltmeter whose range was 150 volts. Connect the battery 
in series with the voltmeter and connect them both across the light- 
ing mains, say an 80-volt circuit. If the voltmeter showed 78.5 
or 81.5 volts, it would indicate that the battery had added or sub- 
tracted 1.5 volts, depending on how its poles were connected, and 
therefore the E. M. F. of the battery must be 1.5 volts. 

Uses of the Testing Set. 

The uses of the Queen- Acme testing set are taken from the circu- 
lar issued by the makers of this instrument, Queen & Co., and which 
is furnished with the instrument. 



Measurements 705 

To Measure Resistance. — Resistances are measured with the 
Queen- Acme as follows : 

Connect the terminals of the resistance to be measured to the 
line posts C and D, and place the battery connectors on the two 
upper tips. This throws one cell of the battery into circuit, which 
is sufficient until balance is roughly attained. Now unplug the 
100-ohm coil in each bridge arm, and place the commutator plugs 
for either high or low resistances. Remove plugs from the rheostat 
until the aggregate resistance unplugged is, as nearly as may be 
guessed, equal in value to that of the unknown resistance. Then 
press the battery key, and, holding that down, momentarily press 
the galvanometer ke} r . If the galvanometer needle swings toward 
-f-, the resistance unplugged in the rheostat is too high and should 
be reduced. If the deflection is toward — , the resistance is too low 
and should be increased. By altering the resistance in this way a 
value will soon be found wherein a slight change either way will 
reverse the deflection of the galvanometer needle. The rest of the 
battery may now be put in circuit by placing the right-hand battery 
connector on the lower left-hand tip. If the keys be again pressed, 
first the battery key, then the galvanometer key, a greater deflection 
will be obtained than before for the same variation in the rheostat, 
and therefore the adjustment can be made more accurately. With 
bridge arms of equal value this is the best result that can be ob- 
tained, but by selecting more suitable values for the two arms a 
considerably higher degree of accuracy may be secured. A refer- 
ence to the following table will show the best values of the bridge 
arms to determine any desired resistance. 

The following table shows the values of A and B respectively, 
to be chosen when measuring any resistance within the range of 
the set : 



Below 1.5 
Between 1.5 and 11 

11 " 78 
78 " 1100 


ohms, 


make A = 1, B = 1000 ^ 
" A = 1, B = 100 f 
" A = 10, B = 100 [ 
" A = 100, B = 1000 J 


Plug for Low. 


1100 ' 


' 6100 




• A = 100, B = 100 \ 


Plug- for Low 
or High. 


6100 ' 

110,000 ' 

1,110,000 ' 


' 110.000 
' 1.110.000 
; 11,110,000 


» 


B = 1000, A = 100 ^ 
" B = 1000, A = 10 J 
" B = 1000, A = 1 J 


■ Plug for High. 



706 Naval Electricians' Text Book 

Placing the Plugs. — In placing the plugs in the commutator it is 
sufficient to remember this : 

First. Excepting when the two arms are of equal value, always 
make arm A the smaller. 

Second. If the resistance being measured is higher than 6100 
ohms, place the commutator plugs for high; if lower than 1100 
ohms, for low. In the first case, the unknown resistance is found 
by dividing the larger bridge arm by the smaller, and multiplying 
the total unplugged resistance in the rheostat by the quotient. In 
the second case, the rheostat resistance is divided by the quotient. 
The arrows on the top of the set facilitate setting the commutator 
plugs. If measuring high resistance, set the plugs in the direction 
indicated by arrow H ; if measuring low resistance, follow direction 
indicated by arrow L. 

Example. — An example will illustrate the method of using the 
bridge. It is desired to measure a resistance say of about 1000 
ohms. Connect the resistance to posts C and D, arrange the com- 
mutator in the direction of arrow L, place battery connectors on 
upper tips, and remove the 100-ohm coil from each bridge arm. 
From the rheostat unplug 1000 ohms, and upon pressing the keys 
the galvanometer needle swings to — . Unplug 100-ohm coil, and 
galvanometer needle swings to +. Try 1050 ohms, moves to — . 
Try 1070, still — . Try 1090, moves to +. With 1080, needle 
reverses again, swinging to — . Try 1085, swings to — . Try 1087, 
it swings to +. Try 1086, swings to — . The true value is, there- 
fore, between 1086 and 1087. To secure more accurate results, 
change bridge arm B to 1000, and remove 10,860 ohms from rheo- 
stat. This proves too little. Try 10,865, and it is found too large. 
It is probable that with 10,000 ohms out no change in deflection 
will be noted smaller than will be produced by a change of 5 ohms 
in rheostat. We see that 10,860 is small and 10,865 large, the true 
value, therefore lies between them, or say 10,863. 

Very Low Resistances. — In measuring very low resistances, ex- 
cellent results may be secured by interpolation. Supposing a resist- 
ance of about .01 ohm is to be measured. Make the bridge arms 
1000 and 1 respectively, and arrange the commutator with the plugs 
in the direction of arrow L. Unplug 10 ohms from rheostat, and 



Measurements 707 

needle swings to +• Try 5 ohms, and it reverses, swinging to — . 
Another trial demonstrates that the correct value lies between 7 
and 8. That is .007 and .008 ohm. Now to determine the result 
accurately note the values of the two reverse deflections when 7 and 
8 ohms, respectively, are out. In the former case the deflection 
is — 1.4 divisions; in the latter case, + 4.1 divisions. The 8 
comes more nearly balancing ; or, in other words, the true value is 
more nearly 8 than 7. Xow divide the larger deflection by the sum 
of the two deflections, and annex the quotient to the smaller value 
removed from the rheostat. -Jf = .56 or .00756 ohm for the re- 
sistance desired. 

To Compare E. M. F's. of Cells. — Connect in all of the cells in 
the set in the usual way, taking care, however, not to reverse them 
by crossing the battery cords. Plug the commutator only between 
B and R, and remove 1000 ohms from bridge arm B. Arm A 
should be all plugged in. From the rheostat unplug say 5000 ohms. 
Xow, connect one of the cells, whose electromotive forces are to be 
compared with its positive terminal, to the + battery post, and its 
negative terminal to the line post C. Upon pressing the keys the 
needle swings one or the other way. If towards + unplug less 
resistance in rheostat, and if toward — add resistance to rheostat. 
A value will quickly be found wherein a variation of an ohm either 
way reverses the deflection. Xow, take this value and add to it 
the resistance unplugged in arm B. This divided by the resistance 
in arm B gives the ratio between the potentials of set battery and 
test cell respectively. It will be noted that the division is decimal 
and consists merely in pointing off as many places as there are 
ciphers in the resistance unplugged from arm B. 

This operation repeated with any number of cells gives their 
values in terms of the battery E. M. F. in the set from which their 
relative values may be obtained. Or, if desired, a standard cell may 
be used to replace the battery in the set, in which case the first 
measurement gives at once the value of the E. M. F. of the test cell. 

If the E. M. F. of the cell or battery being tested exceeds that 
of the battery in the set, it is only necessary to reverse the positions 
of the two batteries, when the results are secured as before. 



708 Naval Electricians' Text Book 

To Check a Voltmeter. — A voltmeter may be checked up, to de- 
termine its accuracy, while in service. Disconnect the battery of 
the set. Connect the circuit to the battery posts of the Queen- 
Acme set, positive lead to + post, negative lead to — post. Be- 
fore doing this, remove say 10,000 from rheostat, plug commutator 
only Between B and R, and remove 100 ohms from arm B. Now, 
connect a standard cell or one whose E. M. F. is known with posi- 
tive terminal to + battery post, and negative terminal to line post 
C. Upon pressing both keys a deflection occurs towards -f- if 
rheostat resistance is too high; towards — if too low. A few 
changes will produce a result wherein a slight variation in the 
rheostat resistance reverses the galvanometer deflection. To find 
the E. M. F. on the line, add 100 to the rheostat resistance and 
point off two. Multiply this by the E. M. F., and the result is the 
desired E. M. F. If the standard is exactly one volt, the total re- 
sistance out represents the E. M. F. on the circuit. 

The attainable accuracy is greater than could be secured with the 
best voltmeter, in fact, it is an excellent method of checking the 
accuracy of all voltmeters. 

Battery Resistance . — To measure internal resistance of a cell, 
first compare its open circuit potential with the potential of battery 
in set as previously explained. Now, shunt it with a known re- 
sistance, say 100 ohms, and again measure its terminal potential. 
The difference between these values, divided by the shunt resistance, 
gives the current flowing. To find the internal resistance, multiply 
the resistance of shunt by ratio between first value measured and 
second. This method has one important feature; it determines 
the internal resistance under normal conditions of use, since the 
shunt may be given any desired value. One is enabled to give a 
low value to the shunt, and make repeated balances while the cell 
is discharging, thereby determining the effect of polarization. 

As an example of the application of the Queen-Acme to the 
internal resistance of a battery, take say a silver chloride testing 
cell and determine its resistance. Measuring its potential in terms 
of test battery, we find it is .212 of the latter. Shunting it with 
1000 ohms, and repeating the measurement we find .179 for the 
terminal E. M. F. The total resistance, therefore, is to the 1000 



Measurements 709 

ohms shunt as 212 is to 179 or the total resistance == }H X 1000 
— 1184. Deducing the shunt we have 184 ohms as the internal 
resistance of the cell. 

To Check an Ammeter. — To check an ammeter with the Queen- 
Acme, secure a low resistance and proceed as follows : Connect the 
low resistance in series with the meter and run leads from it to the 
Queen- Acme set; one lead from the positive side of the + battery 
post, the outer from the negative side to the line post C. Join a 
standard cell between the battery posts; positive to + post, nega- 
tive to — post. Plug commutator between B and R; remove say 
10,000 from rheostat, and 100 from arm B. Balance in the usual 
way by changing rheostat resistance. Now, the difference of poten- 
tial at the terminals of the shunt has been balanced against the 
standard cell, and is found by the directions previously given for 
comparing E. M. F's. to equal shunt 

_ 1.44 X 100 144 

ru — £ + 100 -5 + 100* 

To determine the current flowing, divide this result by the shunt 
resistance. As the shunt resistance has usually a decimal value, it 
is necessary merely to point off in the last operation. 

Use of the Keys. — The primary use of the keys is very evident, 
that in the battery circuit to prevent current from flowing all the 
time, thus running down the battery, and that in the galvanometer 
to protect that when not in use. It has been stated in making a 
measurement, the battery key should be first pressed, and at an 
interval, the galvanometer key. The nature of certain resistances 
may cause the potential of any two points to be widely different 
when the current is starting or stopping and yet they may be at 
the same potential when the current is steady. A current can never 
rise or fall to its full value instantaneously, and when the unknown 
resistance is such that the rise or fall takes place at a different rate, 
the current must be allowed to become steady by first closing the 
battery key, and then closing the galvanometer key. 

In measuring a resistance like that of an electromagnet in which 
there is great self-induction, or a long line in which there is 
electrostatic capacity, the proper use of the keys becomes very 



710 Naval Electricians' Text Book 

important. Although there may be an exact balance, yet if the 
galvanometer key is closed first, the needle may be violently thrown, 
owing to the momentarily induced current. 

In measuring the resistance of an electromagnet, the galvano- 
meter must be placed some distance from it, so it will not be 
influenced by the magnetic field set up around it. The effect can 
be tested by opening and closing the battery switch, leaving the 
galvanometer key opened. If there is any movement at all of the 
needle, it is proof that some part of the circuit is disturbing it, and 
this should be corrected before the measurement proceeds any 
farther. 

Earth Test. — If it is not possible to bring both ends of the un- 
known resistance to the bridge, the test can still be made by con- 
necting one end to the bridge and connecting the far end to a good 
" earth " connection, and also making connection to earth of one 
pole of the battery. The earth being at the same potential, will act 
as though the two were connected to a common terminal. The 
terminal of the bridge where the far end of the resistance and the 
pole of the battery would connect is also connected to earth. The 
measurement is now made as before. 

Uses of the Magneto. 

This instrument finds constant use on board ship for locating 
breaks or faults in circuits, for locating grounds and to a limited 
extent for measuring certain high resistances. It is of particular 
use while wiring circuits and for tracing out breaks in bell circuits, 
and finds use, too, to a certain extent in testing out the various 
windings of a generator or motor, as it quickly locates faults or 
grounds. 

To Test for Open Circuit. — On the outside terminals, there are 
usually connected two short pieces of connecting wires. To test a 
circuit, these leading wires are secured to the ends of the circuit, 
and the armature is rapidly revolved. If the circuit is closed, cur- 
rent flows through the armature, around the electromagnet and 
through the outside circuit, thereby causing the bell to ring. If the 
circuit is broken no current flows and the bell does not ring. 



Measurements 711 

It is always well to short circuit the terminals and then revolve 
the armature to see if all the connections in the magneto itself are 
intact and the circuit continuous. 

To Detect a Ground. — Connect one terminal to the circuit to be 
tested, and the other to a good " ground " or " earth " connection 
through a steam pipe, or to a bulkhead or the ship's side, seeing 
that the paint is scraped off to get connection with the bare iron. 
If there is a ground on the line, current will flow through the 
ground back through the ground connection and the bell will ring. 
If there is no bad ground, the bell will not ring. 

To Locate a Fault in an Open Circuit. — Suppose a break showed 
on one leg of an electric-light circuit. Unscrew all the lamps on 
that circuit and ground both ends of the conductor. Go to a point 
about midway of the line, and at some junction box connect one 
terminal of the magneto to one end of the conductor where discon- 
nected and the other terminal to ground. Eing through. If the 
bell rings, that part of the circuit is complete. Connect the other 
end of the conductor where disconnected to the magneto and ring 
through. If there is no ring, the break is in that part. Connect 
the circuit again and go to some other point in the direction of the 
break and ring through again both ways. A few trials like this 
will soon develop and discover the break. 

To Test for Breaks, Leaks or Grounds in Generator Windings. — 
Treat them exactly as though they were separate circuits, first 
seeing that all circuits are disconnected from one another and the 
brushes raised from the commutator. To see if there is a leak from 
the series winding to the shunt winding, connect one terminal of the 
magneto to the series winding, the other to the shunt, and ring 
through. To test an armature for grounds, connect one terminal to 
the armature through a brush and the other to ground and ring 
through. The connections to be made will readily suggest them- 
selves to obtain the desired result. 

To Measure Resistance by a Magneto. — Each magneto has 
stamped on it the number of ohms through which current can be 
sent and consequently the bell rung. The ordinary resistance 
through which the bell can be rung varies from 15,000 to 30,000 
ohms. Knowing the value for a particular magneto, the loudness 



712 Naval Electricians' Text Book 

of the ringing furnishes a rough idea of the resistance being rung 
through. When the bell rings almost as strongly as when short- 
circuited, it shows the resistance is very low. When it does not 
ring at all, it shows that the resistance is above the value for that 
particular magneto. If it rings feebly, it shows the resistance is 
very high. 

To Increase the Sensitiveness of a Magneto. — Although the re- 
sistance of a circuit may be so high that the bell will not ring 
through it, in some cases the continuity of the circuit may be 
shown by putting the hands in circuit. This is done by putting 
one terminal of the magneto between two fingers and touching the 
back of the hand to the end of the circuit. Wetting the fingers 
and back of the hand will add to the sensation of current. 

Wrong Indications of a Magneto. — As a magneto gets old, the 
permanent magnets are apt to lose some of their magnetism, so the 
voltage for the same number of revolutions grows less, and the 
magneto will not ring through as high a resistance as when new. 
The magneto may be short-circuited and the bell rung through any 
resistance ; or some of the connections may get broken or worn out, 
and the bell not rung through any resistance. 

A magneto may sometimes ring by simply connecting it up to a 
circuit in which there is great capacity, even though the circuit is 
open, thereby giving a wrong indication. There is more or less 
capacity in all parallel circuits, and a magneto will sometimes ring 
when connected to the ends of a long coil of double conductor, such 
as lamp cord, even though the resistance to continuity of circuit 
may be millions of ohms. 

Measurements of Insulation Resistance. 

Insulation resistance may be tested either for the ohmic resist- 
ance of the insulation or for the ability of the insulation to with- 
stand the potential to which it is ordinarily subjected. 

If only the ohmic resistance is required the insulation may well 
be tested by the Testing Set, but for the ability to stand high poten- 
tial as well as ohmic resistance the ohmmeter with a small magneto 
is preferable. 



Measurements 713 

Insulation by Direct Deflection. — Insulation resistance may be 
measured by the testing set by direct deflection. Connect a known 
high resistance, say 100,000 ohms, one terminal to the line post C, 
one terminal to the + battery j^ost. Eemove all plugs from the 
commutator, and have all plugs in the rheostat, as any resistance 
unplugged in rheostat is in circuit with galvanometer and battery. 
Arrange battery tips so as to connect in one cell only. Xow upon 
pressing the keys a deflection of about 8 divisions will be obtained. 
This deflection is due to the current from one cell through 100,000 
ohms. If we multiply the resistance by deflection we have that 
resistance through which one cell will produce a deflection of one 
scale division. This is the constant of the galvanometer. 

Xow, replace the known high resistance by one whose value it is 
desired to know, and add enough cells to produce as large a deflec- 
tion as possible. Multiply the constant of the galvanometer, usually 
expressed in megohms, by the number of cells and divide by the 
number of scale divisions deflection. The result is the desired 
resistance expressed in megohms. 

If a high resistance is not at hand, one may be readily made for 
temporary use by marking with a soft pencil on a strip of ground 
glass. Connect the glass by means of tinfoil ends to the posts of 
the set, and measure its resistance, adding or removing a small 
amount of graphite until the desired value is secured. 

Method by Testing Set. — The following is the method generally 
used as a quarterly test required by the regulations. One leading- 
wire is taken from one terminal of the unknown resistance of the 
bridge to one bus bar on the switchboard. The connections of all 
voltmeters, ammeters and ground detectors are broken, as well as 
connections from the generators, this last effected by leaving the 
main headboard switches open. Another leading wire leads from 
the other terminal of the unknown resistance to a good earth con- 
nection. All lamps in all the different parts of the ship are un- 
screwed from their sockets, and it is well to test each circuit for 
continuity by the magneto, as this will tell whether any lamps have 
inadvertently been left in place. Open all the switches controlling 
the different circuits at the switchboard. When all ready to go on 
with the measurement, close a switch connecting one leg of the 



714 Naval Electricians' Text Book 

circuit to be tested to the bridge. As all connections are broken, 
the circuit can only be completed through grounds or leaks along, 
the one leg of the circuit back to the earth connection to the 
bridge. Measure the resistance by the bridge or at least ascertain 
that it is over some fixed value, say 2 megohms, which it should 
be in a good circuit. Eecord the result. Open the switch and 
close another on the same bus bar, repeat the measurement and 
record it, and so on until measurements on all circuits have been 
made on the same bar, say all the + legs. In the case of search- 
light circuits, see that the carbons are run apart, and in motor 
circuits that the circuits are disconnected at the brushes. 

After finishing all the + legs, disconnect the leading wire from 
the -\- bus bar and connect it to the — bar, and repeat all the above 
measurements, recording the results in tabular form, numbering 
the circuits and distinguishing the legs of a circuit by + an( i — • 

The result of the above measurements will give the insulation 
resistance of each leg of each circuit to earth, and to obtain the 
total resistance of each circuit to earth add the reciprocals of the 
resistances of each leg, and take this receptacle. 

After the above series of measurements has been made, discon- 
nect the leading wire from the earth connection and take it to the 
terminal of the bus bar not already connected. Now close both 
switches of a circuit, leaving all the others open, and all lamps 
being disconnected, current is only established through leaks from 
one leg of a circuit to the other. This is a necessary measurement 
as it might happen that the resistance of each leg to earth was very 
high, but that from one leg to the other was very low. Eepeat this 
measurement for each circuit on the switchboard. 

After this series of measurements is completed, then close all the 
switches and the resistance will be that of all circuits connected in 
parallel, which in the poorest installation should not fall under one- 
half megohm. 

Machine Insulation Resistance. — The testing set can be used in 
a similar manner to test the ohmic insulation resistance of the dif- 
ferent circuits of generators and motors. The different windings 
are disconnected, the brushes raised and connections to the switch- 
board broken. Keeping one terminal of the unknown resistance to 



Measurements 



7J5 



earth, the other may be connected to the different parts and wind- 
ings, and measurements taken and recorded, as from armature to 
earth, series winding to earth, shunt winding to earth, etc. By 
making the proper connections by the leading wires from the bridge 
such insulation resistances can be made, as armature to series wind- 
ing, or to shunt winding, or to 
engine shaft, or to frame, or to 
earth; or from shunt to series, 
shunt to armature, shunt to 
shaft, or such other combina- 
tions as will suggest themselves 
for examining the goodness of 
insulation. 

Method by Drop of Potential 
Using Battery and Voltmeter. — 
The method of using the battery 
and voltmeter is shown in Fig. 
326. 



rn 



<D 



m 



Fig. 326. — Battery Connections for 
Measuring InsulatiQn Resistance. 



Let E — E. M. F. of battery, 
b = resistance of battery, 
X = resistance of voltmeter, 

d x = deflection of voltmeter connected across battery ter- 
minals, 
d 2 = deflection of voltmeter in series with insulation resist- 
ance, 
R = insulation resistance, 
C = current through battery, voltmeter and R, 



then 



or 



C = 



E 



E + X+& 



and C = 



d„ 



R 



E d-, — ■ d .. _ , 

B + X+6 =— g— andg = d *' 



whence 



B = 



(X^b)(d 1 -d 2 ). 



b is so small that it may be neglected. 



71G 



Naval Electricians' Text Book 



Method by Voltmeter. — The method described of measuring in- 
sulation resistance by means of the bridge necessitates stopping 
the generators, or at least cutting off the current from the switch- 
board, but the voltmeter uses the generator current as the source of 
supply. The only instrument required in making this measure- 
ment is a portable voltmeter of known resistance, and the necessary 
connections can be made in a few minutes time, if they are not part 
of the switchboard installation. 




Fig. 327. — Connections for Measuring Insulation Resistance by- 
Voltmeter. 

In Fig. 327 B and B' are the bus bars connected to the gen- 
erator terminals. V is the voltmeter, each terminal having a con- 
nection to earth through the plug switches 1 and 2. The bus bars 
are connected to their respective terminals of the voltmeter through 
the switches s and s'. 



B + 



e 



Ri|C t 

ill 
v 

Ric 



B'- 




Fig. 328. — Voltmeter Connections to Ground. 



The values of the insulation resistance of B and B' to earth may 
be deduced by a consideration of the connections shown in Fig. 328. 






Measurements 717 

When the voltmeter is connected between B, the + side, and 
earth E, there may be leaks from B to E and from B' to E. 
Let V = difference of potential between B and B ', 

V = deflection shown when B is connected to earth, 
V\ = deflection shown when B' is connected to earth, 
X = resistance of voltmeter, 
then 

C t R ± + CR = 7 and C 2 X + C£ = 7, 
CA = <7 2 X =:V—CR = V, G x + C 2 = C. 
The joint resistance of R 1 and X is 

i?,X 



and 



V— V 



or 



F— F 



This shows that the value of E, the insulation resistance of 5' 
to earth, depends on the value of the insulation resistance of B to 
earth. If the voltmeter is connected between B' and earth and 
gives a deflection V\ , a similar deduction will give R x in terms 
of R, thus 

From equations from (1) and (2), the values of R and R ± will 
be found to be 

R = *SZ=r=*D, ( 3) 

and 

l- xtr-p-™ . (4) 

v i 

If the -\- leg is not grounded, V\ = 0, and 

R= x i v-v D> (5) 

and if the — leg is not grounded, V x = 0, and 

R^xv^m. ( 6) 



718 Naval Electricians' Text Book 

Example. 

A direct reading voltmeter, having 16,000 ohms resistance is con- 
nected from the + main to earth. The voltmeter shows 2.6 volts and 
the difference of potential between mains is 110 volts. Find the insula- 
tion resistance between the — main and earth, assuming that the 
insulation resistance of the + main to earth is (1) infinite; (2) the 
same as the — main to earth, and (3) one-tenth of the — main to earth. 

If the insulation resistance of the + main is infinite, that leg is not 
grounded, and from equation (5) 

R = X(V ~~ Y ' ) =16,000 X 110 ~ 2 - 6 = 660,900 ohms. 
V 2.0 

Under condition (2) V = Y\ and from equation (3) 

r = X(V — ^—V'J = 16> ooo X 110 ~ 5 - 2 = 644,900 ohms. 
Under condition (3) V'^lO V, 
and R = XiV ~Z,~ Vl) =16,000 X 110 ~ 28,6 = 500,900 ohms. 

Suppose it is required to measure the insulation resistance of 
the — legs to earth. One circuit is taken at a time, the others 
being cut out ; both section switches on the bus bars are closed. 
The switch s' is closed and plug switch is inserted in 1. The only- 
current then through the voltmeter is from the -{-, bus bar through 
the voltmeter, through the switch 1 to earth and from earth to 
earth leaks along the — leg, and thence to the — bus bar. All 
the — legs can be tested in this way in a few minutes, recording 
for each circuit the reading of the voltmeter. 

To test the -f- legs, take one circuit, keep both section switches 
closed; close s, open s' and insert plug in 2. The current is then 
from -f- bus bar to leaks along the -)- leg to earth to the voltmeter 
through 2, through the voltmeter and switch s to the — bus bar. 
Eecord the reading of the voltmeter and do the same for each leg. 

The bus bar voltage can be determined by opening both 1 and 2 
and closing s and s'. Having this voltage and the drop due to 
earth leaks, we have the data necessary for calculating the insula- 
tion resistances. 

Knowing X and V and assuming a value for R beyond which its 
actual value is not desired, V can be calculated. If a reading 
shows above this calculated value, R is less than the assumed value, 
and vice versa. 



Measurements 719 

Suppose it was not wished to know the actual resistance, provided 
the resistance to be measured was over 2 megohms, and the volt- 
meter had a resistance of 13,000 ohms, and we were using an 80- 
volt circuit then 

2,000,000 = 13 >°y,x so _ 13;000j 

or 

„ 1,040,000 . .. ,. n 

v = plpoo = * volt P ractlcall - v - 

If the voltmeter showed \ volt or less, the insulation resistance 
for the particular part measured would be 2 megohms or over. 

This is a very rapid and easy method and the insulation of the 
different legs of the different circuits to ground can be tested at 
any time while the generator is running, and besides it has the 
advantage of the high potential of the running machine. The 
only observations are V and V for each measurement and these can 
be recorded for each circuit, and the calculations can be made after 
the tests are finished, the whole operation only consuming a few 
minutes. 

Method by Ohmmeter. — To measure insulation resistance by this 
method requires the use of an ohmmeter and a magneto. The lead- 
ing wires from the magneto are connected to the proper terminals 
on the ohmmeter and -the circuit to be tested is connected to the 
other set of terminals. The same preliminary operations as in the 
other methods are necessar}^. If one leg is to be tested to earth, 
one terminal is connected to the leg and the other terminal to 
earth. The armature of the magneto is rapidly revolved and cur- 
rent is sent through the ohmmeter and circuit, being completed 
through grounds or leaks. The ohmmeter measures directly the 
resistance of the circuit being tested, and the result is read off 
directly from the scale. This is by far the most rapid and con- 
venient method of making this test, and not only is the ohmic 
resistance of the insulation measured, but the circuit is tested for 
its ability to stand the high potential developed by the magneto. 

It sometimes happens that the resistance measured with a low 
potential differs from the same resistance measured with a high 
potential, due to the electrostatic attraction of the conductors under 
the influence of high potential. 






720 Naval Electricians' Text Book 

The magneto and ohmmeter can be used to test out the different 
windings and insulation resistance of the various parts of gener- 
ators and motors in a way similar to that described for the magneto 
alone, and under the heading " Machine Insulation Resistance." 

Measurement of the Resistance of Generator Windings. 

As an illustration of the general methods of measuring resist- 
ances by the use of instruments furnished to ships, a general 
description will be given of the measurement of the resistances of 
the different parts of a compound generator; namely, the shunt 
winding, the series winding and the armature. These values are 
usually furnished as part of the data when the generators are 
installed, but it may become necessary to verify them, or to make 
the measurements in testing for faults or breaks. 

The Shunt Winding — By the Bridge. — The resistance of the 
shunt field is usually sufficiently large to be measured by means of 
the bridge, the ends of the winding being disconnected from the 
generator terminals and connected to the terminals of the bridge 
for the unknown resistance. It requires some skill in making this 
measurement, as when current is sent around the shunt coils or the 
circuit is broken at the key, the momentary self-induction reacts on 
the needle of the galvanometer and gives it a motion which is not 
its true motion due to the current flowing arbund it. This can be 
obviated to some extent by keeping the battery key pressed down 
some time before the galvanometer key is pressed, and releasing 
the latter key before the battery key. In making this measure- 
ment by the bridge, if possible the balance arms should be equal, 
so that the resulting reading in the rheostat arm may not have any 
error multiplied or divided. 

By Voltmeter and Ammeter. — A more satisfactory way of meas- 
uring this resistance is by means of a voltmeter and ammeter, con- 
necting the former to the shunt field terminals and disconnecting 
one end of the field windings and inserting an ammeter in series 
with it. 

Then start the generator and let it build up to its full voltage, 
and the instant it has attained this voltage, read both the volt- 
meter and ammeter. Dividing then the number of volts by the 



Measurements 



721 



number of amperes will give at once the resistance of the shunt 
winding in ohms. It is necessary to take the readings the moment 
full voltage is reached, because the moment current flows around 
the shunt coils, heat is generated in them, thereby increasing the 
resistance. The first readings will give the cold resistance, or the 
resistance of the copper itself. It is usually necessary to know the 
hot resistance of the shunt winding, which is calculated by taking 
the readings of the voltmeter and ammeter after running for two or 
three hours. If the field has four shunt spools, the total resistance 
divided by four should give the resistance of each spool, though it 
is always better to check the measurement by shifting the volt- 
meter to the terminals of each field spool separately, leaving the 
ammeter in circuit as before. 




Fig. 329. — Connections for Measuring Resistance of Series Winding. 



Series-Winding Resistance. — The resistances of the series wind- 
ings and armatures of generators and motors are so small, usually 
less than .01 of an ohm, that measurement by the bridge is not 
satisfactory. The method generally practiced and which gives good 
results, is the fall of potential method. This method of measuring 
the resistance of an armature has been given under the heading, 
"To Measure a Eesistance with Voltmeter and Standard Eesist- 
ance," but the following method is a little more practical and with 
more details: 

The connections for making measurement of the series winding 
of a generator are shown in Fig. 329. For this measurement, cur- 



722 Naval Electricians' Text Book 

rent is taken from the switchboard, or some convenient mains or 
feeder, being energized by another running machine. The stand- 
ard resistance a, ~b, is connected in series with the series winding, 
and in addition, a resistance e is inserted in series, to steady the 
current and to prevent short-circuiting the running machine. The 
standard resistance a, ~b, should have a resistance somewhat near 
the supposed resistance of the unknown resistance, say .01 ohm. 
The resistance e can readily be made of lamps, so arranged in series 
and parallel as to give almost any desired result and being heavy 
enough to withstand the heavy currents. 

Only enough current is required from the running generator to 
give a good readable deflection on the voltmeter, and it is well to 
insert an ammeter in circuit, as shown at A, in order to know just 
what current is flowing. It is best to start with a low-testing 
current and gradually work up to the value decided on. 

A low-reading portable voltmeter is used and is connected to the 
terminals a and h, and the current varied by changes in the lamp 
bank until a good deflection is obtained. The final reading of the 
voltmeter is recorded and the current being kept steady, the volt- 
meter is connected to the terminal of the series winding and the 
reading noted. With the three known quantities, the two readings 
of the voltmeter and the known resistance, the unknown resistance 
is calculated by the formula previously given, 

V'R 

from which it is seen that the accuracy of the measurement depends 
on the accuracy of the known resistance. 

For very low resistances a current of 10 to 100 amperes may be 
necessary and a voltmeter reading to thousandths of volts. 

Armature Resistance. — The same method can be used to de- 
termine the resistance of an armature, by disconnecting two ends 
from the commutator and connecting them in series with the known 
resistance, or by connecting the brushes in circuit with the resist- 
ance. If the last method is used, the brushes must make good 
contact with the commutator, and all other connections broken, and 
the value obtained will depend on the number of brushes and on 
the manner in which they are connected. 



Measurements 723 

Contact Resistances. — The fall of potential method, with a high 
resistance, low-reading voltmeter, may be nsed to determine the 
goodness of contacts in binding screws, or from terminal leads to the 
brushes, or from the brushes to the commutator. Good contacts 
should show very low resistances which would be indicated by low 
readings of the voltmeter. 



CHAPTER XXXI. 
FAULTS OF GENERATORS AND MOTORS. 

A generator or motor considered simply as a mechanical machine 
is a very simple affair and the parts in which troubles may arise 
are few in number, the only moving or wearing parts being the com- 
mutator, brushes and bearings. To make it a complete electrical 
machine, to these may be added the armature core with its wind- 
ings and the field pieces with the field windings. 

Troubles may occur in any of these parts due either to faults 
within the machine itself, or to faults occurring outside the ma- 
chine, in the external load that the generator or motor is supplying, 
the effects being conveyed to the machine and manifested there. 

Every fault has its effect and the same effect may be traced to 
widely different faults, and a fault may produce one or more differ- 
ent effects. In order to definitely determine the proper relation 
between faults and effects, we may either tabulate the faults and 
trace the effects, or tabulate the effects and assign to them the faults. 

The following table is self-explanatory and shows how intimately 
the different faults are connected, and with its help the cause of 
any particular fault may be traced. 



1. Too high 
voltage. 



Too low 
voltage. 



1. Too high speed of engine. 

2. Too strong magnetic field. 

1. Too low speed of engine. 

2. Too weak magnetic field. 

3. Brushes not properly set. 



HOW MOST READILY DETECTED. 



1. Voltmeter reads greater 

than standard, and lamps 
burn with undue bril 
liancy. 

2. Same. 



1. Voltmeter shows lower than 

standard and lamps burn 
dimly. 

2. Same. 



3. Same. 



1. Slow the engine. 



2. Introduce more resistai 
in shunt field. 



1. Increase speed of engine. 



2. Take out resistance in shi 

field. 

3. Rock rushes back a 

forth till highest volta 
is shown. 



Faults of Generators and Motors 



725 



Excessive 1. Too many lamps burning or 
current. motors running. 



2. In a motor, too much me- 

chanical work being done 
by it. 

3. In a dynamo, too much 

power being absorbed by 
motors in circuit. 



4. Short circuit; leak or 

ground in external circuit. 

5. Short circuit in armature 

coil. 

6. In a dynamo, by excessive 

friction in bearings of a 
motor or by motor arma- 
ture striking pole pieces. 
In general any cause tend- 
ing to slow motor. 

7. Grounds in armature. Two 

grounds to the core 
amount to a short circuit. 



Excessive 
sparking 
at brushes. 



1. Excessive current; there- 

fore due to any of the 
causes given under that 
head. 

2. Brushes improperly set. 



3. Brushes make poor contact 
with commutator. 



4. Rough, non-concentric com 

mutator. 



5. " High " or " flat " bars in 

armature. 

6. Broken circuit in armature 

or commutator. 



7. Weak field magnetism, 
caused by broken circuit 
in field winding or short 
circuit in same; two or 
more grounds in windings; 
reversal of one or more 
field coils. 



8. Unequal magnetism. 



HOW MOST READILY DETECTED. 



By too high reading of am- 
meter for capacity of ma- 
chine. 

By excessive sparking of 
motor brushes and too 
high reading of motor 
ammeter. 

By excessive sparking of 
dynamo brushes and too 
high reading of dynamo 
ammeter. 



By excessive sparking of 
brushes, and heating of 
whole armature. 

By heating of short-cir- 
cuited coil more than the 
others. 

By sparking of dynamo 
brushes. By sound of ar- 
mature striking while run- 
ning. By heating of mo- 
tor bearings. 



7. Same as 5. 



3ame as given under 
cessive current." 



By the sparking itself and 
heating of brushes. 

Same, and by sighting un- 
derneath between brushes 
and commutator. 

By the sparking. A rough 
commutator can be de- 
tected by lightly touch- 
ing finger nail to it while 
running; an eccentric 
commutator by the regu- 
lar rise and fall of the 
brushes. 

By the jumping or vibra- 
tions of the brushes. 

Commutator flashes, and 
nearest the break is cut 
and burnt. Flashing con- 
tinues when armature is 
slowly turned. 

Dvnamo fails to generate 
full E. M. F. 

If very weak, motor runs 
very slow. 



One brush sparks more than 
the other. 



Cut out necessary number 
of lamps or reduce motor 
current. 

Reduce the load on the 
motor. 



Reduce load on motor cir- 
cuits. In this case, none 
of the motors may be do- 
ing too much work, but 
there may be too mam- in 
dynamo circuit. 

Locate and remove leaks or 
grounds. 

Stop machine. Locate coil. 
If entirely burnt out, must 
be renewed. 

File away pole pieces of 
motor, or recenter arma- 
ture. 

Clean and oil journals, or 
refit bearings. 

Locate the grounds. Rein- 
state the coils contain- 
ing them. 



1. Same as given under 
cessive current." 



Shift the brushes backwards 
or forwards till sparking 
is reduced to a minimum. 

Adjust, file or clean brushes 
until they rest evenly on 
commutator with light 
but even pressure. 

Smooth commutator with 
fine file or fine sandpaper. 
If eccentricity is due to 
uneven wear of bearings, 
renew or reline them. 



Same as above, or turn 
down the commutator in 
lathe. 

Locate coil by drop of po- 
tential method. If in com- 
mutator, bridge over the 
break. If in armature 
coil, it must be renewed. 

Short circuits or grounds 
are easily located and 
remedied if external to 
the windings. If internal, 
faulty coil must be re- 
wound or repaired if only 
grounded. 

A reversed coil will lower 
the voltage instead of in- 
creasing it, and it is rem- 
edied by reversing the 
connections. 

Only remedied by reshap- 
ing pole pieces. 



726 



Naval Electricians' Text Book 



5. Heating of 
armature, 



Heating of 
commutator. 



7. Heating of 
field coils. 



8. Heating of 
bearings. 



Dirty commutator, causing 
brushes to vibrate, partic- 
ularly if of carbon. 

10. Poor brushes, especially if 
of high-resistance carbon 
hard blisters forming on 
them. 

11. Vibration, especially of 
brush holders, causing 
rapid vibration of brushes. 



1. Excessive current through 

it and therefore due to 
any of the causes given 
under that head. 

2. Eddy currents in core. 



3. Conduction from other 
parts as from commutator 
or bearings, the heat being 
conveyed to armature. If 
from commutator, bars 
may be too small. 



1. Too great pressure of 

brushes, friction causing 
heat. 

2. Excessive sparking. 



3. Excessive current. 



4. Conduction from other 
parts. 

1. Excessive current in field 
circuit, due to short cir 
cuits or grounds. 



2. Eddy currents in pole 
pieces, heat being con 
ducted to the coils. 



1. Lack of lubrication. 

2. Dirty or gritty bearings. 

3. Bearings out of line. 

4. Rough or cut shaft. 

5. Shaft bent. 



HOW MOST READILY DETECTED. 



Flashing around commuta- 
tor. 

10. By ragged appearance of 
brushes around edges and 
formation of hard spots. 

11. By a humming, singing 
sound of brushes. 



Same as given under "Ex- 
cessive current." 



Core becomes hotter than 
armature coils after run- 
ning for a short time. 

Other parts connected to 
armature, as commutator, 
shaft or bearings, hotter 
than the armature. 



1. By feeling the commutator 

with the hand. 

2. Same. 



!. Same. 



4. Same. 



1. Too hot to bear by the 

hand. If exceedingly hot, 
by smell of burning shel- 
lac or varnish or char- 
ring cotton. 

2. The pole pieces are hotter 

than the coils after 
short run. 



1. By feeling with hand. Oil 

cups empty or feeding 
pipes clogged. 

2. By feeling with hand. 

3. Unequal wear of bearings, 

and shaft will not turn 
freely by hand. 

4. Shaft will show the rough- 

ness in the bearings. 

5. Unequal wear in bearings 

and armature will wobble. 
Very hard to move by 
hand. 



9. Clean commutator (metho< 

given later). 

10. Renew brushes. 



11. Reduce cause of vibratic 
or give the brushes a li 
tie greater pressure c 
commutator. 



1. Same as given under 
cessive current." 



2. Only remedied by better d 
sign of core lamination. 

Locate source of heat r. 
thermometer or feel t 
the hand, and correct 
by cleaning and lubrici 
tion. 



1. Reset brushes. 



2. Discover the cause of spar 

ing and correct it, accor 
ing to the particular cau 
given under sparking. 

3. Discover cause of excessh 

current and correct a 
cording to particular cau 
already given. 

4. If from bearings, lubrica 

or refit them. 



1. Locate the particular co 

in which fault lies and r 
pair or rewind. Metho< 
given later. 

2. Only remedied by bett< 

design. 



Fill oil cups; clean feedin 
pipes. 

Remove cap and thorough! 

clean. 
Bearings must be lined 11 

or shells rebabbitted. 

very serious, new bearing 

will have to be made. 
Turn down shaft in lath 

or if not too bad, reduc 

by filing. 
Shafts can only be straigh 

ened by disconnects 

from armature and rehea 

ing and reforging. 



Faults of Generators and Motors 



727 



Too low 
peed (refer- 
ing to mo- 
ors). 



Too high 
peed (refer 
ing to mo 
ors). 



Dynamo 

'ails to 
generate 
E. M. F. 



1. Too much load. 



. Any of the causes given 
under " Heating of bear- 
ings " causing excessive 
friction. 

3. Weak magnetic field and 
heavily loaded. 

4. Short circuit or grounds in 
armature. 



5. Too low voltage at ter- 
minals. 



1. Too light load (in series 

motors). 

2. Weak magnetism (if lightlv 

loaded). 

3. Too high voltage at ter- 

minals, due to high volt- 
age of dynamo. 



1. Too weak residual magnet 

ism, caused by a jar or 
reversal of current not 
sufficient to reverse mag 
netism. 

2. Short circuit within ma 

chine, or grounds in field 
windings. 

3. Reversed field coils. 



I. Series and shunt windings 
connected up opposite to 
each other. 



Brushes not properly placed. 



6. Open circuit due to broken 
wire, brushes not oi 
commutator, switch open 
connections loose, fuses 
burnt out. 



1. By speed indicator; heavy 
sparking, heating of all 
parts and bearings. 

2. Same, and same as given 
under " Heating of bear- 
ings." 

3. See cause 7, under " Ex- 
cessive sparking." 

4. By motor taking excessive 

current without load as 
shown by ammeter or 
heavy sparking and heat 
ing. 
. By motor voltmeter or 

speed indicator. 
By heavy sparking and heat 
'ing. 



1. By noticeable increased 
speed. 
Same. 



Motor fails 
to start 



HOW MOST READILY DETECTED. 



3. Same. 



Decrease E. M. F. at ter- 
minals of motor or reduce 
the work to be done. 

Discover particular cause 
and remedy same as given 
under " Heating of bear- 
ings." 

Same as 7 under " Ex- 
cessive sparking." 

Same as under 5, " Exces- 
sive current." 



By correcting line voltage. 



1. Increase load. 

2. Same as 7 under heading 

" Excessive sparking." 

3. Correct line voltage by 

remedies 1 and 2 under 
" Too high voltage." 



1. Very little attraction by 1. Send a current through field 



1. Too much load. 



2. Excessive friction, due to 
any causes given under 
heading " Heating of 
bearings." 



the pole pieces when test- 
ed with a piece of iron 



2. Magnetism very weak. 



All poles should have al- 
ternate magnetism; if a 
coil is reversed, it will 
show magnetism, but may 
not be of opposite polar- 
ity. 

Voltage falls as speed is 
increased, the external 
circuit being closed, show- 
ing that they are working 
against one another. 

Magnetism and E. M. F. 
increased by shifting the 
brushes. 

If break or loose connec- 
tion is in machine, mag- 
netism will be very weak. 
If in external circuit, ma- 
chine will show its regu- 
lar magnetism and volt- 
age at the terminals. 



1. No motion and fuse in cir- 

cuit melts or circuit- 
breaker acts. See if mo- 
tor runs all right when 
light. 

2. Same, and motor hard to 

turn when not loaded, and 
with no current. 



from a few cells or from 
running dynamo. 



Locate the grounds or short 
circuits and correct them. 

Make polarity opposite by 
reversing the connections 
of the coil. Each pole 
should be opposite to the 
one on each side of it. 

Reverse connections of 
either field, but not both. 



Find central position by 
experiment or from draw- 
ings of connections. 

Make diligent search out- 
side of machine. If in ma- 
chine, test the circuits 
with magneto for conti- 
nuity. Set up on all con- 
nections. 



1. If motor does not start at 

once, turn off current and 
search for cause. Reduce 
load on motor. 

2. Remedies same as given un- 

der " Heating of bear- 
ings." 



728 



Naval Electricians' Text Book 



FAULTS. 


CAUSE. 


HOW MOST READILY DETECTED. 


REMEDY. 




3. Short circuit of field or ar- 


3. Motor refuses to revolve, 


3. If connections are ma 




mature or among connec- 


though shows signs of 


wrong, consult make 




tions. 


strong magnetism. Will 


diagram and correct the 






turn easily by hand if un- 


Test for continuity a 






loaded and with no cur- 


short circuits as gn> 






rent. If current is very 


later. 






great, it is indication of 








short circuit. If fault is 








in field, magnetism will 








be weak. 






4. Open circuits due to field 


4. Weak magnetism shows a 


4. Turn current from mot 




switch open, fuse melted, 


loose connection in field 


and search for cause 




loose or broken connec- 


circuit ; no magnetism, 


discontinuity; examine 




tions, or some fault at 


that field switch is open. 


switches, fuses and c( 




generator. 


May be heavy current in 


nections, tautening all. 






armature. 


Test for continuity in n 






If there is no armature cur- 


chine circuits and rep 






rent there will be no spark 


broken or burnt-out coi 






at brushes when raised. 




13. Flickering 


1. Uneven running of engine, 


1. By flickering of lamps or 


1. Overhaul engine, especia 


of lamps. 


probably due to governor 


vibration of voltmeter in- 


governor. 




failing to properly func- 
tion. 
2. Loose connections, either 


dicator. 






2. Same. 


2. Examine all connectk 




on machine, switchboard 




and see that they are fi 




or external circuit. 




and make good contact 



CHAPTEK XXXII. 

TESTS FOR AND LOCATION OF FAULTS. 

Under the heading Remedy given in the table of the preceding 
chapter most of the remedies given are simple and explain them- 
selves, as for instance : Kemedy No. 1, under Fault No. 1, " slow 
the engine/' which would of course be done by throttling down the 
steam ; No. 2, " Introduce more resistance in shunt field," which 
would be done by a proper manipulation of the field regulator. 
Some, however, are but indicated, as No. 4, under Fault No. 3, 
" Locate and remove leaks or grounds," and *it is the purpose of 
this chapter to enter a little more into the detail of the simple 
tests and the location of the faults. 

Short Circuit in External Circuit. 

This would be indicated by the melting of the fuses in that cir- 
cuit, or possibly by the melting of the main fuses or by the opening 
of the circuit breakers. After determining the circuit on which the 
short is, an examination along it, if accessible, may lead to its 
location. If not, it can be tested for by the magneto or ohmmeter, 
by unscrewing all the lamps and opening the circuit at different 
points and ringing through both ways. Working from the switch- 
board, try the feeder first by disconnecting at the feeder junction 
box. By connecting the ohmmeter to the two ends, its resistance 
can be roughly measured ; that is, it is either very high if the short 
is not there, or infinitely small if it is. By opening the circuit at 
various points, the short can be located within limits and further 
observation will accurately determine it. 

The short circuit indicated by the melting of the circuit fuse 
would show that it was either on the feeder or mains; for each 
branch being protected, if it occurred in a branch it would only 
burn out the branch fuse. Short circuits in the external circuit 



730 



Naval Electricians' Text Book 



do usually occur in branches and particularly in portables, but then 
they are easily located as the branches are short. Most of them 
are due to moisture in the wiring accessories, or to the insulation 
being torn from portable wires, or burnt by hauling over hot coals 
or ashes. 

Grounds in External Circuit. 

A ground on an external circuit would be indicated by the ground 
detector, either of two kinds or both being connected to the mains. 

Lamp Detector. — This, with its connection, is shown in Fig. 330. 

A represents a positive bus bar, and B a negative bus bar, from 
which lead circuits through the ship. 1 and 2 are two incandescent 




B a 

Fig. 330. — Connections of Lamp Ground Detector. 



lamps connected in series across the bus bars. Between the lamps 
there is a connection to earth marked G, with a plug 3 to make 
the connection to earth complete. C and D are lamps on a circuit. 
If there are no grounds on the circuit, the lamps 1 and 2 will burn 
with equal brilliancy, but reduced candle-power, as with the same 
E. M. F. there is double the resistance, so only half the current 
flows through each lamp. If a ground occurs on the negative leg 
of the lamp circuit, the current will now flow from the + Dar 
through 1, but will avoid the high resistance of 2, so will take a 
path through ground to the ground on the main as at 67', and thence 
to the — bar. The result of this is that 1 now has full current and 
will burn with full candle-power, while 2 will be extinguished. If 
it is only a slight ground, both lamps may burn but with unequal 



Tests for axd Locatiox of Faults 



731 



brilliancy. If the ground was on the positive leg, the current would 
now avoid 1, taking the path through ground G" to G through 2 to 
the — bar, and 2 would burn with increased brilliancy while 1 was 
lowered if not extinguished. 

With several circuits closed from the bus bars and a ground ap- 
pears, it becomes necessary to discover on which circuit it is, and 
this is done by cutting out the circuits, one at a time. On cutting 
out a circuit, and the ground disappears, it must have been on that 
circuit. On locating the circuit, keep that circuit in and cut out 
all the others. Then pull out the portables on that circuit one at 
a time, and if the ground disappears when a certain one is pulled 
out, the ground must have been on that particular portable, and it 
may then be sought and found. 




w^ 



Fig. 331. — Connections of Voltmeter Ground Detector. 



Grounds generally are due to moisture in the junction boxes or 
wiring accessories, or to the slipping of connections in lamp sockets, 
by which a bare wire may touch the outside shell which in turn 
may rest against some grounded conductor. A fruitful source of 
grounds is in the portable ventilating fans, the support frequently 
touching some exposed part of the leading wires. 

Of course, grounds may occur in the mains, due to moisture 
rotting the insulation, and this can be tested for with the magneto, 
connecting one end to the main, the other to a ground and ringing 
through. 

Voltmeter Detector. — Fig. 331 represents the typical connections 
for using a voltmeter to detect grounds. V is a double-reading 



732 Naval Electricians 7 Text Book 

voltmeter with the zero in the middle of the scale, the indicator 
being deflected to the right or left, depending on the direction of 
the current through it. One terminal is connected to a contact 
piece fitted with a switch by which it may be connected to either 
bus bar of the generator, A or B and the other terminal is con- 
nected to a ground through a plug switch. 

If connected as shown to the positive bar and there are no 
grounds on the negative side of any of the circuits, there will be 
no current through the voltmeter and no deflection, or the reading 
will be zero. If there are any grounds on the negative side, as at 
G', current will then flow from the + bar through the voltmeter 
to ground G to G' and to — bar. If it is dead ground, the full 
difference of potential between the bars will be indicated; if only 
a slight ground, the fall of potential, owing to the high resistance, 
will be very small. 

Connected to the negative bar, any grounds on the positive side 
of the circuit will be detected, the current then being from the 
positive bar through the ground, as at G" , through ground G, 
through voltmeter to negative bar; the indicator now deflecting in 
an opposite direction to that of the first case. 

The method of locating the particular circuit on which the 
ground exists is exactly the same as with the other ground de- 
tector, and also the same procedure is necessary to further locate 
the ground in the circuit. 

The method of calculating the ground resistance is given on 
page 717. 

Short Circuit in Armature. 

A short circuit in the armature usually attracts attention by the 
smell of burning varnish or shellac. When this is discovered, the 
armature should be stopped at once, and felt all over by the hand, 
the short-circuited coil being much hotter than any of the other 
parts. A piece of iron held near a revolving armature with a 
short-circuited coil will be strongly affected once a revolution, as 
the coil passes the iron. If a large part of the armature is short- 
circuited, it is not so easy to distinguish the parts by the heat, so 
some fall of potential method is resorted to. 



Tests for axd Location of Faults 



'33 



One way is to pass a strong current through, opposite commutator 
bars and measure the difference of potential between the points 
where contact is made with the commutator. Then connect one 
terminal of a portable voltmeter to one connection and the other 
terminal to the different bars of the commutator. If the arma- 
ture is sound, there should be the same fall of potential from the 
leading-in point to bars each side equally distant from it. In 
this way the fall of potential from bar to bar may be determined, 
and the fall should be regular, and if between any two bars there 
is a smaller fall of potential than the average it shows the presence 
of a small resistance, or probably the short-circuited coil. 

A short-circuited armature coil can only be remedied by re- 
winding. 

Short Circuit in Field. 

Usually a short circuit is confined to the windings of one spool; 
the effect of which will be to cause weak magnetism in the short- 
circuited coil, and a piece of iron held at an equal distance between 
poles will be more strongly attracted by the good one than by the 
weak. 

A short-circuited coil will cause the resistance of the total field 
to be much reduced, and this can be detected by roughly measuring 
with the bridge. The fall of potential ( 

method can be used to detect the spool 
in which the short circuit is. 

Suppose the coils are represented by 
a, h, c, d, e and /, in Fig. 332, and a 
source of current is connected to 1 and 

4. Pleasure the fall of potential be- 
tween 1 and 4, between 1 and 6, 1 and 

5, 1 and 2, 1 and 3. The fall between 
1 and 6 should be the same as between 
1 and 2 ; between 1 and 5 the same as 
between 1 and 3, and consequently be- 
tween 5 and 6, and 4 and 5 the same as 

between 2 and 3, and 3 and 4. If this symmetry does not exist 
between any two coils, then that coil must be the short-circuited 
one. The short-circuited coil should be cooler than the others. 




Fig. 332.— Testing for Short 
Circuit of Field Windings. 



734 Naval Electricians' Text Book 

Grounds in Armature. 

A single ground in an armature is not a source of trouble, but 
two or more, especially in the same coil, become a short circuit 
with its evil effects. The particular coil in which grounds to the 
core exist may be determined by connecting all the commutator 
bars together by wrapping them with a conductor and passing a 
current through this wire, taking the other leading wire to the iron 
core. Current then flows through the armature coils through the 
grounds to the iron core, thus magnetizing the coil in the vicinity 
of the grounds, and these points can be detected by a small compass 
needle moved around the armature. 

Grounds in Field. 

The effect of grounds in the field is to short circuit a coil, and 
they can be detected and located in the same manner as a short- 
circuited coil. 

Fracture in Armature. 

This can usually be detected by violent flashing on the com- 
mutator, the commutator bar nearest the break being burnt or 
cut. A bad case of high or low bars may produce this same flash- 
ing, but if produced by this cause, it will disappear when the arma- 
ture is slowly revolved, which will not be the case if caused by a 
fracture. 

A fracture can be detected by a magneto which will not ring 
through a broken circuit, and can only be found by fall of potential, 
the same as in detecting a short circuit in armature. A voltmeter, 
one terminal connected to the leading-in wire, will not indicate 
when connected to adjoining bars until it has passed the break, 
for up to that time there has been no complete circuit, but when 
one terminal is on one side of the break and the other terminal on 
the other, the circuit is complete, and the fall is indicated. The 
fractured coil must lie between the commutator bars where one 
does not indicate and the adjoining one does. 

In case of armature-coil fracture no particular coil will be heated 
more than another ; if anything, the fractured coil being cooler than 
the others, as the current does not flow through it. 



Tests for and Location of Faults 



735 



Fracture in Field Winding. 

If there is a complete fracture of both the series and shunt wind- 
ings in a compound generator, it will probably refuse to excite. 
The test for fracture can be made with the magneto, and the coil 
containing the fracture detected by fall of potential. 

Suppose in Fig. 333 a, b, c, d, e and f 
represented the field coils in a six-pole 
machine, and that they were connected 
with a source of current at the termi- 
nals marked + and — . If there was a 
break in a coil, say in e, a voltmeter 
connected to 7 and 6 would not indi- 
cate ; nor would it if connected to 7 and 
5, but if connected to 7 and 4, it would 
indicate, the circuit now being com- 
plete, showing the voltmeter had 
bridged over the break in coil e. If 
there was also a break in d, connection 
between 7 and 4 would show no cur- 
rent, but would between 7 and 3. Connection between 3 and 4 
would show no indication if there was a break in both d and e, but 
would if it was only in d alone. If breaks were in both d and e 
connection between 3 and 5 would show current, and in this way it 
can be determined absolutely in which coils breaks occur. 

If the fracture is outside, it is comparatively easy to repair, but 
if internal, the coil would probably have to be rewound. Ex- 
cessive vibration sometimes carries away the connections between 
the spools and they are apt to break off under the outside layers. 




Fig. 333. — Testing for Frac- 
ture in Field Winding. 



To Test for Magnetism. 

Magnetism can be detected by any magnetic material, such as a 
piece of iron or steel or iron tool, as screw-driver or knife, being 
approached to a supposed magnet. Magnetism will be shown by 
the iron held in the hand being attracted, requiring at times con- 
siderable force to hold it away from the magnet. To detect very 
weak magnetism a small compass needle is used, being deflected 
by the very faintest trace of magnetism. 



736 Naval Electricians' Text Book 

The polarity may be determined by the compass needle, by re- 
membering that like poles repel and unlike attract. 

To Test for Speed. 

This is done by the use of a tachometer, which by applying its 
shaft to the shaft of the rotating armature indicates at once the 
number of revolutions. Or a speed indicator is applied to the end 
of the armature shaft and the number of revolutions made in a 
given time is counted. 

To Test for Heat. 

Under the table of faults, by far the greatest number of faults 
fall under the general head of heating, such as heating of armature, 
heating of commutator, heating of field coils, heating of bearings, 
and even the faults due to excessive current and excessive sparking 
are mostly faults due to the heat produced by them. 

Remarks on Heating. 

The expression excessive heat is one that requires a little more 
definite limits, for what might seem excessive to one might not be 
to another. 

The amount of heat that is allowed in the armature coils and 
field windings above the temperature of the surrounding air is 
limited by specifications, but the degree of heat that is positively 
injurious is easily determined by feeling the various parts. If the 
heat in any part of the winding is greater than the hand can stand 
for a few seconds, then it is higher than a safe limit. If the hand 
can stand the heat for two or three minutes, it is usually not con- 
sidered excessive. If there are any signs of smoke or smell of 
varnish or shellac or rubber, the temperature is far too high. The 
only way to cool heated parts is to stop the machine, except possibly 
in the case of bearings, where water might be used. 

For accurate results as to temperature, the thermometer should 
be used on the parts, the bulb covered with waste and the highest 
reading recorded taken. To find the heat or temperature in the 
field windings, calculations should be made from the cold and hot 



Tests for and Location of Faults 737 

resistances by knowing the per cent increase per degree rise of 
temperature. 

In considering the heat in any portion of a machine, it is very 
necessary to locate the exact source of the heat. Every or any hot 
part may not be the real cause, but the heat may have been con- 
ducted there from other places. A hot bearing might make a hot 
commutator or armature and vice versa. In locating heat troubles 
the very hottest parts should be sought, as they are very likely to 
be the source of trouble. If a certain part heats under certain 
conditions, it is likely it will do so again under the same condi- 
tions. To discover the parts that heat first, it is better to start with 
the machine absolutely cool in all its parts, and then after a short 
run to feel all over for the hot parts, for in a short run, there will 
not be time for the heat formed to be conducted to other parts. 
After a long run, only general temperatures can be obtained, but it 
cannot be told with certainty just what the source of heat is, for 
there is a general distribution all over the machine. 



CHAPTER XXXIII. 

TELEPHONES. 

The underlying principle of the telephone is the increase or de- 
crease of intensity of an unbroken electric current, and in order to 
transmit sounds of the voice over an electric conductor it is neces- 
sary that a current be caused to flow in the conductor and that the 
intensity of the current is in accord with the vibrating movements 
of the sound-producing body. 



3A 



Fig. 334. — Simple Telephone Connection. 



The early invention of the telephone is illustrated in Fig. 334. 
In its simplest form it consists of a permanent bar magnet A, A' 
at each end, with one end of each surrounded by a coil of fine wire 
B, B' in series with the line connecting the stations. A soft-iron 
diaphragm C, C is mounted close to one end of each of the mag- 
nets. When a sound is made in front of the diaphragm, it vibrates 
in exact accordance with the sound waves striking against it. The 
vibrations produced by the voice are transmitted by the air to the 
diaphragm and this latter vibrates back and forth in front of the 
magnet. These vibrations of the diaphragm produce backward and 
forward movements of the lines of force which pass into the 
diaphragm and which are due to the permanent magnet. The 
magnetic field between the pole of the magnet and the diaphragm 
is shown in Fig. 335. 

Some of these lines of force cut across the coil B, first in one 
direction and then in the other and induce currents in it. These 









Telephones 739 

very feeble currents are transmitted by the line to the other end, 
where those in one direction pass around B' in such a direction as 
to increase the strength of the permanent magnet A', and the 
attraction which it exerts on the dia- 
phragm C is thus increased. Oppo- 
site currents pass around B f in the 

reverse direction and weaken the mag- « _\}V,'i 

net A', diminishing the attraction on -I ^ < 

C. When C moves in one direction, 
C moves in one direction and when C 
moves in the opposite direction, C" 

reverses its direction. One therefore „ "~Z~ _, ,. „. ., . 

Fig. 335. — Magnetic Field at 

vibrates in unison with the other and Telephone Receiver, 

the receiver sends out waves exactly 

like those that fell upon the sender, and a sound made at C is 
reproduced at C". 

As long as sound waves impinge against C , alternating currents 
of varying intensities pass over the line and increase or decrease the 
strength of the permanent magnets. No battery is used in this 
circuit, the only currents being the induced currents caused by the 
lines of force cutting across the coils on the ends of the magnets, 
and which are so feeble that only the most sensitive instruments can 
detect them. 

Variable Resistance Transmitters. 

The source of the induced currents in the simple telephone cir- 
cuit above described is due to the energy of the sound waves, and 
in consequence of which they are very feeble and such a trans- 
mitter could have no practical value except for very short dis- 
tances. The early experiments to secure a practical transmitter 
were along the lines of causing variation in the strength of current 
produced by some outside means, the variation always remaining 
in accordance with the movements of the diaphragm. A battery 
was used and the transmitter was so designed as to cause variation 
in its current strength by changing the resistance in the battery 
circuit. 



740 Naval Electricians' Text Book 

Edison Transmitter. — One of the first practical transmitters was 
devised by Edison and carbon was the substance by which the resist- 
ance of the circuit was varied. Carbon pieces in contact vary in 
their electrical resistance according to the pressure with which they 
are held together. The first type consisted of a platinum " disc 
secured to the diaphragm bearing against a button of compressed 
plumbago. The circuit was completed through this contact which 
was varied by greater or less pressure on the plumbago button 
caused by variations in the sound waves striking the diaphragm. 
This change of resistance caused variations in the current that 
passed over the line to the receiver. 

Hunning's Transmitter. — In Hunning's receiver the variable re- 
sistance medium consists of a quantity of finely-divided carbon 
granules held between two conducting plates, and through which 
the battery current flows. This form has a large number of imper- 
fect contacts and the change in resistance is caused by the change 
in the pressure with which the granules are held together. The 
diaphragm is so arranged as to press more or less against these 
carbon particles and thereby produce changes in resistance which 
cause currents of varying intensities in the line. 

Nearly all successful transmitters are modifications of this type. 
Hughes' Microphone. — This type of sound transmitter or sound 
multiplier depends on the variations in resist- 
ance of an electric circuit caused by loose con- 
tact of electrodes. The elementary principles 
are illustrated in Fig. 336. 

C is a sounding board holding two cup- 
shaped contacts A, A of carbon, between which 
lightly rests a carbon strip B, which makes 
imperfect contact at A, A. These are connected 
to a battery in which a receiving instrument is 
Fig. 336.— Hughes' Eluded. The slightest noise, imperceptible to 
Microphone. the unaided ear, sets up vibrations which dis- 
turb the contact of A and B, and so sets up 
variable currents in the line which are reproduced in the receiver 
with great distinctness. The clearness and distinctness of the 
sounds vary with the pressure, and as this is gradually increased, 




Telephones 741 

the sounds become weaker, though always clear, until when the con- 
tact is perfect the sound ceases. 

This indicates that it is not the resistance of the carbon itself 
which changes under pressure, but the change of resistance is caused 
by the imperfect contact at the carbon electrodes. 

Of the different theories advanced for the explanation of the 
change of resistance of carbon under pressure, the most probable 
one is that the change of resistance is due to the variation of the 
area of contact, and in the granular form it is the variation in the 
number of granules in contact. An increase of pressure increases 
the area of contact, lowers the resistance and allows greater current 
to flow, while a decrease of pressure produces the opposite effect. 

Carbon Transmitters. 

Of the variable resistance transmitters mentioned in the preced- 
ing section, those made on the principle of the Hunning's transmit- 
ter have been the most successful, for no substitute for carbon as 
the variable resistance medium has been discovered. Carbon has 
all the properties requisite for telephonic or microphonic work; it 
produces change of resistance by surface contact; can be easily 
made into the desired form; it does not oxide or corrode; it is 
abundant and cheap. 

The form of transmitter almost universally used in this country 
in the early days of telephones was the Blake transmitter. In this 
a platinum pin is pressed by a light spring against a polished plug 
of hard carbon, forming an imperfect, delicate contact through 
which the current flows. This mechanism is mounted behind the 
usual disc which takes up the vibration of the voice, and greater 
or less pressure is brought on the contact of the platinum pin and 
carbon, the varying resistance producing the requisite varying in- 
tensity of the line current. 

This transmitter is very delicate and transmits the quality of the 
voice in an excellent manner, but it lacks in power. 

Many forms of the carbon granular type have been made, and 
although all present peculiarities, the general principle of construc- 
tion is the same, and a description of one will render clear the 
action of the others. The type of transmitter in general use by the 



'42 



Naval Electricians' Text Book 



American Bell Telephone Company is known as the White trans- 
mitter, and is spoken of as a " solid-back " type. Its general 
construction is shown in Fig. 337. 

The front, A, is of metal, forming with the back, B, a complete 
metallic casing for the working parts of the instrument. The 
diaphragm, D, is of aluminum, held by a soft-rubber ring E, and 




White " Solid-Back " Transmitter. 



against which are held two damping springs, F, only one of which 
is shown. C is a metallic block, hollowed out to form an enclosure 
for the electrodes, and is held rigidly in place by a supporting 
bridge, which is secured to the metal front piece. The inner cir- 
cular wall of C is lined with paper, and screw-threaded into its 
inner face is a metallic piece, I, against which rests the back elec- 
trode of carbon, J. The front electrode, also of carbon, K, is 



Telephones 743 

carried on a metallic piece, L. On the flange of the piece, L, is 
carried a mica washer, M, held in place by the screw nut, N, and 
the washer is of sufficient diameter to cover the cavity in the block, 
C, when the front electrode is in place. 

The space between the two electrodes is filled with granular 
carbon, and as the electrodes are slightly smaller in diameter than 
the cavity, the space around them is also filled with the granules. 
There is sufficient space left to allow for the expansion of the 
granules due to the heat of the current, and this form allows a 
large current without undue heating. 

When the carbon granules have been put in the cavity and the 
front electrode is in position, the mica washer is slipped in and the 
nut, N, is screwed in place; after which the cap, 0, is screwed on, 
binding the washer firmly against the face of the block, C, and con- 
fining the granules in the cavity. 

The screw-threaded portion, P, of the piece, L, passes through a 
hole in the center of the diaphragm and is held in place by the 
nuts, R. The vibration of the diaphragm is conveyed to the front 
electrode, which can move against the elasticity of the mica washer, 
while the back electrode is firmly held, and thus more or less 
pressure is brought to bear on the carbon granules between them. 

The back electrode is in metallic connection with the back of the 
instrument which forms one terminal, while the other terminal is 
mounted on an insulating block, 8, and is connected to the front 
electrode by a flexible connecting wire. 

Receivers. 

The typical form of telephone receiver is shown in the elementary 
sketch in Fig. 334, and it might be said that the receivers used in 
modern practice are but developments of the single permanent mag- 
net, with one end wound with a coil of fine wire. 

In the first days of telephone work, the receivers were of the 
single-pole type. In general they consisted of a compound bar 
magnet formed of two pairs of magnetized steel bars, placed with 
their like poles together. Between the bars at one end is clamped 
a soft-iron pole piece, and at the other a similarly-shaped iron 
block. The soft-iron pole piece forms the core of a coil of wire 



744 



Naval Electricians' Text Book 



which is slipped over it, and near this coil is secured the vibrating 
diaphragm. The whole is mounted in a conveniently-shaped rubber 
shell, formed of two pieces, one enclosing the magnets, and the other 
screwing into it and holding the diaphragm in place. Heavy lead- 
ing-in wires run from the coil along the inside of the rubber shell 
to terminal pieces at the bottom which project through and form 
outside terminals to which the line wires are connected. 



HL 



m\ 




Fig. 338. — Bell Telephone Receiver. 



Bipolar Receivers. — The object of bipolar receivers is to 
strengthen the field in which the diaphragm vibrates by presenting 
both poles to the diaphragm, and the lines of force 'are concen- 
trated near the point where they are most effective. There have 
been as many different forms of receivers made as transmitters, but 
the governing principle remains the same, and the construction of 
one successful receiver will illustrate all the principal points. Such 
a form used by the Bell Companies is shown in Fig. 338. 

In Fig. 338 are shown two magnets, M and M', secured at one 



Telephones 745 

end by screws through an iron tail block, A, and at the other end 
by a threaded brass block, B. The pole pieces, P , P f , carry the 
coils, G, C , and are clamped between the pole end of the magnets 
and the block, B. This block screws into a threaded portion in the 
rubber body of the shell and by turning it the magnet poles are 
moved nearer to or farther from the diaphragm, and after once 
being adjusted, it is held by a pin through the shell. The binding 
posts, D, are fitted with lock-nuts and there is an eyelet, E, fitted to 
take the strain cord, so no strain will come on the terminals if the 
receiver should happen to fall. In order to give sufficient weight 
to properly work the hook switch, a lead weight, L, is clamped be- 
tween the magnets. The diaphragm is secured between the two 
pieces of rubber shell. 

Watch-Case Receivers. — In some classes of work it is necessary 
to hold the receiver constantly at the ear, so that the hands may 
be free, as in wireless telegraphy, fire control or switchboard work. 
For such purposes a special form of receiver that can be held in 
place over the ears has been devised and from its shape and small 
weight it has been called the " watch-case n or " head " receiver. 

These are fitted with either one or two receivers, to cover either 
one ear or both, and are made with straps to go over or around the 
head to hold them securely in place. 

The permanent magnets are circular in shape and of the ring type 
and are cross magnetized to produce poles on opposite sides of their 
circumferences. Circular pole pieces which carry the coils are 
secured to the ring magnet and their pole faces rest close to the 
diaphragm as in the ordinary receivers. The working mechanism 
is mounted in a hard-rubber shell and the diaphragm is secured 
between this shell and the ear piece. 

Use of Induction Coils. 

The first practice in connecting telephonic instruments was to 
connect the transmitter, the receiver and battery at one station 
directly in the line leading to the other station, considering for 
the present but two stations. The change in resistance of the whole 
line, whereby currents of varying intensities were produced to 
actuate the receivers was caused bv the change of resistance in the 



746 



Naval Electricians' Text Book 



transmitter. In case of a long line this change of resistance was 
very small in comparison to the whole resistance and the currents 
were consequently very feeble. To remedy this difficulty, Edison 
proposed to use an induction coil with the primary in the circuit of 
the transmitter. 

The connection of the induction coil is shown in Fig. 339. 

T represents the transmitter in series with the battery B and the 
primary T of the induction coil, I" the secondary of the induction 
coil is in series with the receiver B and the line L ± L 2 . The trans- 
mitter in this connection is operating in the low resistance of the 
primary circuit, rather than over the resistance of the whole line, 




Fig. 339. — Connection of Telephone Induction Coil. 



and any change of resistance caused by the transmitter bears a much 
larger ratio to the resistance of the primary circuit than it does to 
the resistance of the whole line, consequently, for the same voltage, 
the changes of current will be proportionately larger in the primary 
and the induced currents in the secondary that pass over the line 
will be proportionately greater. The fluctuations of current pro- 
duced by the induction coil are many times greater than could be 
produced by the transmitter alone. 

Another advantage of the induction coil is that the primary 
being of few turns while the secondary is of many, the induced cur- 
rents in the secondary have a very high voltage as compared to those 
in the primary, and transmission can be effected over much greater 
length of line and over much higher resistance than if the trans- 
mitter was used alone. 



Telephones 747 

Calling Apparatus. 

Before conversation can be carried on between points, there must 
be some means adopted by which a person at one station can attract 
attention at the other. Ordinary vibrating call bells or buzzers are 
used, fitted with separate lines and batteries, or the talking battery 
may be used over separate lines, or over the talking lines. For long 
distances, ordinary batteries will not furnish sufficient current to 
operate call bells, and in some cases, they have been used with in- 
duction coils, using the high voltage of the secondary windings to 
furnish the desired current. 

In many systems, especially in that known as the local-battery 
system, a form of generator is used that is very similar to the mag- 
neto shown in Fig. 316, Chapter XXIX. This furnishes alter- 
nating currents of high voltage and actuates a vibrating bell at the 
called station. 

In central stations using the " local-battery " system attention is 
called by the ringing of the call bell, and at the same time by the 
dropping of a shutter which indicates the number of the calling 
station. 

In the " common-battery " system, the attention of the operator 
is called by the lighting of an incandescent lamp by the operation 
of the caller removing the receiver from the hook. 

Local-Battery System. 

This system, as its name implies, has a local battery at each sta- 
tion to furnish the talking current. The system is classified under 
two heads, series and bridging. The series system is used when a 
number of instruments are used in series on the same circuit, and 
the bridging system where the instruments are placed in multiple 
or bridged across the line. This last is the more common practice. 

The calling and talking apparatus operate over the same line, 
and when the circuit is complete for one operation it must be open 
for the other and vice versa, and means must be provided for 
effecting this result. It is now universally accomplished by a 
switch actuated by the weight of the receiver, and when the re- 
ceiver is hanging in its provided place, the talking circuit is cut 
out and the calling circuit is closed ready to operate for calling. 



748 



Naval Electricians' Text Book 






At each station in this s3 T stem there must be provided the trans- 
mitter, receiver, induction coil, battery, switch, bell and generator. 
It is customary to place the generator, the bell, the switch and the 
induction coil in one box and the battery in a separate box. 

The connections for a complete station on the bridging system is 
shown in Fig. 340. 




Fig. 340. — Bridging Circuit. 



In Fig. 340, R is the receiver ; T , the transmitter ; B, the battery ; 
F, the primary of the induction coil ; S, the secondary ; B', the bell ; 
(}, the generator; II, the hook switch, and 1, 2, 3, the terminals. 
The line terminals are connected to 1 and 3. The position of the 
hook switch, H, shown, is accomplished by hanging the receiver on 
it. In this position it will be seen that the talking battery is cut 
out and the circuit open, and the station is ready for a call. The 



Telephones 749 

bell, B', is bridged directly across the line and incoming current 
finds but the one open circuit, that through the bell. The gener- 
ator, G, is across the line, and its circuit is broken at a, but is made 
by the operation of turning the handle of the generator. 

To call from this station, it is only necessary to operate the 
generator and current goes over the line past the bell terminals to 
the called station, the talking circuit being open. After being 
called; to talk, it is only necessary to lift the receiver from the 
hook switch and the battery terminals are connected through the 
transmitter and the primary of the induction coil. The terminals 
of the secondary are connected by the same operation to the line 
through the receiver. 

The above description is that of an ordinary " wall set " connected 
on the multiple or bridge system. In the series system, the call 
bell is connected to the line when the receiver is on the hook, and is 
cut out when the receiver is lifted clear. 

The connections for " desk sets " are practically the same as for 
the " wall sets," different dispositions being made of the induction 
coil, calling apparatus and battery. 

Common-Battery System. 

In the Local-Battery System, it is usual to make use of the mag- 
neto for calling central, but in the Common-Battery System sig- 
nals are made by simply lifting the receiver from the hook and 
replacing it. In some types of signals, lifting the receiver has the 
effect of lifting a target within sight of the operator and holds the 
signal displayed until the receiver is hung again on the hook, when 
the target drops in place, either by its own weight or under the 
action of a spring. 

The modern method is to use a small incandescent lamp which 
is illuminated as soon as the hook is released by taking off the 
receiver. To signal any station from central requires some kind of 
a sound apparatus to attract attention, and current to operate this 
must come through the same line as the talking circuit. The 
signal apparatus must be in a condition to be energized at any time 
while the receiver is on the hook and consequently when there is no 
connection between the two sides of the line. 



750 



Naval Electricians' Text Book 



An alternating current provides the necessary solution of this 
problem, as it does not require a continuous metallic circuit, and 
it is practically done by interposing a condenser in series with the 
bell across the line. This bell is energized by a magneto at the 
central station, the condenser allowing the alternating current pro- 
duced to pass through it, while it acts to keep the current of the 
common battery at central open. 

The illuminating lamp at central may be placed either directly 
in series with the common battery and the line, or in a relay cir- 
cuit, which is thrown in only when the battery circuit is estab- 
lished by lifting the receiver. In the former case, the resistance 
of the signal-bell magnets is sufficient to prevent enough current 
from flowing to illuminate the lamp, but when the receiver is 




Fig. 341. — Common-Battery Telephone Circuit. 



raised, the battery current flows through the low resistance of the 
transmitting circuit and produces sufficient current to light it. 

As the name of this system implies, there is but one battery and 
that is installed at the central. This battery furnishes current for 
talking as well as for the signal apparatus at the central. 

The complete connections from a station to central are illustrated 
in Fig. 341. 

The station on the left (Fig. 341) represents one station and that 
on the right, the central, connected by the two lines L ± and L 2 . A 
battery, B, of about 25 volts is kept connected at central to all the 
lines entering it, but no current flows from this battery as long as 
the receivers, E, are on their hooks, H. In that condition there is 
no circuit for the direct current of this battery, as the condenser, C, 
acts as an infinite resistance to it. If central wishes to call the 
station, it is only necessary to throw upon the line an alternating 



Telephones 751 

circuit which passes into and out, or through the condenser. This 
is done by turning the handle of the magneto generator, G. As the 
alternating current flows through the coils of the bell magnets, 
m and m , the armature which is pivoted at a is drawn first towards 
m and then towards m' ', vibrating back and forth between the bells 
B', producing a ringing sound. 

If the station wishes to call central, it is only necessary to lift 
the receiver R from the hook H. This closes the line circuit at t 
and allows current from the battery B to flow in the line through 
the transmitter. At the same time the current flowing energizes the 
electromagnet g, and its armature is attracted, closing the lamp 
circuit containing the lamp I at &. This illuminated lamp at- 
tracts attention of the operator who moves a switch to connect the 
central telephone to the calling station. As the calling station 
talks into the transmitter the strength of the battery current through 
the primary /' of the induction coil is varied by the varying pres- 
sure produced on the diaphragm of the transmitter. These varia- 
tions induce in the secondary I" of the induction coil the talking 
currents which pass over the line to the receiver of the operator. 
By this arrangement the primary and secondary currents pass over 
the same line but it does not interfere with the distinctness of 
speech. 

When the operator finds what station is required, it is rung up 
and connection is made with it by a plug e containing a flexible 
cord, which is pushed into the contacts c and d. When the con- 
versation is over the receiver is replaced on the hook which breaks 
the battery circuit and the lamp at central is extinguished. The 
operator then disconnects the two stations. 

Switchboards. 

Telephone switchboards are used for interconnecting telephone 
lines centering at a common point. The two general systems, 
Local-Battery or Magneto System and Central-Battery System 
require each a different arrangement of the talking and calling 
apparatus, though they contain certain parts that are common to 
each. 

The terminals of all lines entering the exchange at the switch- 



752 



Naval Electricians' Text Book 



board are secured to spring jacks, by which the line may be con- 
nected to another by the insertion of a ping in the jack. These jacks 
are small switch sockets, and so arranged that both lines of the 
metallic circuit are continued in a flexible cord by the insertion of 
the plug. This is generally accomplished as follows and can be 
seen in Fig. 342. One terminal of the line is secured to a circular 
ring which forms the socket for the plug, and the other terminal 
ends in a spring contact. The plug is so constructed that its tip 
end makes contact with the spring contact of the line terminal while 
the body of the plug forms a sleeve and makes contact with the ring 
socket. The tip and sleeve of the plug are insulated from each 
other and the terminals of the flexible cord are secured, one to each. 



ft 




P T BL K -t^ 






Fig. 342. — Magneto Switchboard. 



Cord circuits are common to switchboards used with the two 
principal systems. Ordinarily it is a term which refers to two 
plugs with the connecting flexible wire and the necessary calling 
and talking apparatus by which an operator may answer a call or 
complete a connection with any line. In magneto switchboards a 
cord circuit consists of two plugs adapted to fit the spring jacks, 
with the connecting cord ; a listening key by which the operator can 
connect the central talking apparatus so that conversation may be 
had with either one or both communicating stations, and a ringing 
key by which the central magneto is connected to one of the plugs 
and the station whose jack is plugged may be called. 

Magneto Switchboard. — The essential parts of a magneto switch- 
board are shown in Fig. 342. The lines on the left are those from 
distant stations and all end in the spring jacks, J, J. In the lower 
line is shown the calling apparatus with which each line is provided. 
It consists of an electromagnet energized by currents produced by 



Telephones 753 

the generator at a calling station, which pass over the line and 
around the electromagnet. When the core becomes magnetized, it 
attracts its armature, shown to the left, and which is pivoted at 
the ripper end and connected to the rod above the magnet. This 
rod ordinarily holds in place the front target which is hinged at its 
lower end. As the armature is attracted, the target is released and 
drops, exposing the number of the calling station. 

The cord circuit consists of the two plugs, P and P', fitted as 
above described with tip and sleeve contacts to engage the spring 
jacks, J, the flexible cord, C, C, and the talking and calling appa- 
ratus. The general operation of calling and talking would be as 
follows: Suppose the lower station calls by turning his magneto 
handle. This throws an alternating current on the line and on the 
electromagnet at central becoming magnetized, the armature is 
attracted and the target drops. On seeing the number of the call- 
ing station, the operator pushes the plug, P, into the spring jack, J , 
and presses the listening key, L. This connects the operators 
talking circuit in series with the line circuit of the calling station 
and disconnects the signal circuit, by the tip of the plug raising 
the spring contact, S. On finding the number of the station de- 
sired, the operator pushes the plug, P' , in the jack of the desired 
number and presses the calling key, K. This connects the central 
generator, G, to the line of the desired station, and on turning the 
handle of the generator, current is sent over the line and rings the 
bell at the desired station. When the calling key is depressed, the 
talking circuit is cut out, by means of the spring contacts shown 
at K, so the alternating current of the generator cannot go over the 
line of the original calling station. When the desired station is 
obtained the ringing key is raised and the two stations are now 
connected for conversation. 

There is usually fitted, in addition, another electromagnet across 
the cords circuit, C, C, which is actuated by current from either 
station while the jacks are still plugged to indicate that the con- 
versation is finished. 

Common-Battery Switchboard. — The circuits of a modern com- 
non-battery switchboard as developed by the Western Electric Com- 
pany are shown in Fig. 343. The leads L 1 and L 2 (heavy lines) 



754 



Naval Electricians' Text Book 



are connected to a station, and another station, which could be 
shown on the right would be exactly similar. The cord circuit for 
the switchboard embraces all the portion between the plugs P and 
P', and in addition the switchboard also embraces the circuit shown 
on the left under the heavy lines L X L 2 of the calling station. A 



r-O 



Ify 



L 2 Li 



.CO 



*B 



^g-^ 





S.R.-- 



fefj>- 



Fig. 343. — Elements of Common-Battery Switchboard. Western Elec. Co. 



station on the right, or called station, would have an exactly simi- 
lar equipment at the switchboard. 

To signal the operator, the calling station takes the receiver from 
the hook. Circuit is then completed from the battery B' through 
the line relay, LE, through the primary of the induction coil at 
the calling station and the two armatures of the cut-out relay, CO. 
As soon as the line relay magnet is energized, it attracts its arma- 
ture and closes the circuit of the line lamp, LL. This circuit is 



Telephones 755 

completed by the armature and one side of the battery being 
grounded, as shown at E. The operation of removing the receiver 
at the calling station thus results in lighting the line lamp, LL. 
When the operator sees this, plug P is inserted in the jack, J, and 
battery B is thrown on the line. The plug has a third strand con- 
nected to the sleeve of the plug with connections as shown through 
a supervisory lamp, SL, and resistances. When the plug is in- 
serted, current from battery B flows around an electromagnet, SB, 
called the supervisory relay and the effect is to attract its armature 
and cut out the lamp SL, through the resistance shown. Thus the 
supervisory lamp is not lit as long as the receiver is off the hook at 
the calling station. 

Another effect of entering the plug P in the jack, J, is to cause 
the line lamp to be extinguished. This is accomplished as follows : 
Current from the ungrounded side of battery B flows through the 
coil of SB, which is then energized and attracts its armature which 
completes the circuit to the sleeve of the plug through the resist- 
ances in line and around the lamp. From the ring of the jack cur-^ 
rent flows around the electromagnet, CO, known as the cut-out 
magnet, to ground. This energizes the electromagnet, CO, and its 
armatures are attracted, breaking the circuit to the line relay. The 
electromagnet LB being no longer magnetized, its armature is 
drawn away by the action of a spring and consequently the circuit 
through the line lamp is broken. 

When the plug P is in the jack and the receiver is off the hook at 
the calling station, current from the battery B is flowing through 
the two strands of the cord through the plug and jack over the line 
and through the transmitter of the calling station, thus energizing 
it and putting it in a condition to vary the intensity of current by 
the changes in its resistance caused by the sound waves striking the 
diaphragm. 

After the operator inserts the plug in the jack, the listening key, 
L, is closed, which throws the central's transmitter and receiver in 
line with those of the calling station and conversation may be 
effected. When the desired number is obtained, the plug, P' , is 
inserted in the proper jack, and the calling key, K, is closed, which 
connects the generator circuit to the desired station, and at the same 
time cuts out the cord circuit to P, so the calling current cannot 



756 Naval Electricians' Text Book 

produce any signal at the calling station. When the called station 
answers, the ringing key is opened which connects P' to the circuit 
again and the two stations are now connected through, the cord cir- 
cuit and conversation can take place. 

When the conversation is over, the receivers are hung on the 
hooks at each station, with the result that the supervisory lamps 
SL, one for each station, are lighted, which allows the operator to 
know that the call is finished. On withdrawing the plug, P, the 
lamp, SL, on that side is extinguished and in withdrawing P' , the 
one on the right is extinguished. The above operations are accom- 
plished as follows: When the receiver is hung on the hook, the 
circuit of battery B is broken at that point, and consequently the 
magnet SR ceases to be magnetized and its armature is drawn away, 
breaking the shunt circuit around the lamp. Current now flows 
from the ungrounded pole of the battery through the lamp 8L to 
the sleeve contact on the plug and through the cut-out relay to 
ground and to the grounded pole of the battery. Finally, on with- 
drawing the plug from the jack, the circuit on that side is broken 
and the lamp is extinguished. The same operation holds good for 
the station on the other end of the cord circuit. 

Repeating Coils. — The coils CC and C'C shown in Fig. 343 are 
called repeating coils. Though they are shown as four separate 
windings, they are in reality wound on one core. The object of this 
winding and of inserting the battery in parallel with the talking 
stations is as follows : By this arrangement current from the bat- 
tery divides at the junction of the coils C and C and part goes to 
the instruments at each station and for a given difference of poten- 
tial at the battery a greater current will flow in each portion of the 
cord circuit than if the battery was connected in series. The cir- 
cuit in which change of resistance is caused by the transmitter is 
only that from a station to the switchboard, consequently it bears 
a greater ratio to the resistance of the line than if the change in 
resistance took place in the whole line connecting the two stations 
and the fluctuations of current are correspondingly greater. 

A change in the current of either circuit produced by a trans- 
mitter acts inductively through the repeating coil of the other cir- 
cuit and causes corresponding changes of current to act on the re- 
ceiver of the other line. Thus, when the left-hand station is trans- 



Telephones 757 

mitting, coils C and C act as primary coils and coils C and C as 
secondary coils, and the opposite is the case when the right-hand 
station is transmitting. 

Interior Telephones. 

Interior telephone circuits are used where a number of people 
located close together desire a complete intercommunication with 
one another. There are several systems that have been devised to 
meet different requirements and they are generally classified under 
the following heads : 

1. General Intercommunicating System. 

2. Common Talking-Circuit System. 

3. Central Switchboard System. 

In the Intercommunicating System each station can make its 
own connections without a central operator. This requires that at 
least one wire for each telephone be connected to every telephone 
on the system, and besides these, other wires are necessary, depend- 
ing upon the plan of wiring adopted. It differs from the Common 
Talking- Circuit System in that as many conversations can take 
place at the same time as there are pairs of instruments, while the 
Common Talking Circuit only allows one conversation at a time. 

In the Central Switchboard System the services of an operator are 
necessary and this system does not differ much from regular city 
exchanges except in the number of the telephones. 

Intercommunicating System. — As an example of a successful 
means of interior communication, a system using the '" Ness Inter- 
communicating Telephone" and manufactured by the Holtzer- 
Cabot Electric Company is given. This telephone is provided with 
a switch which automatically returns to the home point when the 
receiver is hung upon its hook. 

This system is usually wired according to one of the following 
plans : 

1. Local talking battery, central ringing battery. 

2. Local talking battery, magneto ringing. 

3. Central talking and ringing batteries. 

Each of these plans has its own advantages, and each requires a 
different number of connecting wires as shown in the accompanying 
diagrams. 



7D1 



Naval Electricians' Text Book 



Fig. 344 shows a system using a local talking battery with a cen- 
tral ringing battery. In addition to a wire for each station two 
additional wires are required. 

If No. 1 station wishes to call No. 4, the switch moving over the 
circular arc is moved until it rests on terminal marked 4. The 
button of the switch is then pressed, which rings the bell or buzzer 
at station 4. As soon as the receivers are off the hooks the local 
battery is thrown in circuit and talking takes place over the line 




Fig. 344. — Local Talking and Central Ringing Battery. 



connecting the two stations and one of the two extra wires. The 
primary circuit is complete through the heavy lines which include 
the transmitter. The secondary circuit is completed as follows: 
Starting from the left-hand terminal of the secondary marked S, 
current flows through No. 1 receiver, to the terminal marked T at 
No. 1, to the connecting wire marked T, to terminal T at No. 4, 
through No. 4 receiver, through secondary, to the hook switch at 
No. 4, then to the blank terminal under the ringing switch, to the 
blank terminal above the numbered ones, then to No. 4 connecting 
wire, to terminal No. 4 at No. 1, to ringing terminal No. 4, then 



Telephones 



759 



through the switch to the' hook switch and from there to the right- 
hand terminal of the secondary, completing the circuit. 

When station No. 1 is communicating with No. 4, No. '2 could 
be in communication with No. 3. As soon as the calling station 
has finished the conversation, the receiver is hung upon the hook 
which returns the calling switch to the home point, and it is now 
ready to receive a call from any other station. 

Fig. 345 shows a system using a local talking battery with mag- 
neto call. In addition to the wire for each station, only one addi- 
tional wire is needed. 




Fig. 345. — Local Talking Battery with Magneto Call. 



If No. 1 station wishes to call No. 3 (Fig. 345), the ringing 
switch is moved to the terminal marked 3 in the curved row of ter- 
minals under the switch, and the magneto handle is turned. This 
throws an alternating current on the line and rings the bell at No. 
3. The circuit is as follows: from the left-hand terminal of the 
magneto to the extra wire between stations, to the corresponding 
terminal of the magneto at No. 3, past the magneto and through 
the bell magnets, then to the terminal strip under the hook switch, 
to the adjoining terminal held together by the switch, to the blank 
ringing terminal under the ringing switch, to the blank terminal in 
the other curved row, then to No. 3 wire, back to No. 3 terminal 
in the curved row, to No. 3 ringing terminal, through the ringing 



760 



Naval Electricians' Text Book 



switch to the hook switch, to the terminal switch under the hook 
switch, through No. 1 bell and back to the magneto. 

As before, when the receivers are clear of the hooks, the talking 
battery is thrown on the primary circuit containing the transmit- 
ters, and the talking currents flow through the wire connecting the 
two stations and the extra wire. 

When the hook is returned to its place at No. 1 station, the 
switch automatically returns to the home point. 




Fig. 346.— Central Talking and Ringing Battery. 



Fig. 346 shows a system using both central talking and ringing 
batteries. In addition to the wire for each station, three extra 
wires are necessary. 

From what has been said regarding the other two systems, this 
should be readily understood and the ringing and calling circuits 
followed. It will be noticed that the primary and secondary cir- 
cuits of the talking circuit are entirely separate from each other, 
the current from the battery dividing and going through the pri- 
mary circuit at each station. The currents induced in the second- 
ary only flows through the receivers. 



Telephones 



761 



It is usual to make all the wires connecting the stations and such 
extra wires* as may be needed in one cable, each wire being insu- 
lated from the other, and the whole completed cable insulated. 
The wiring from the instruments and connection terminals is made 
in one cable and lead to connection boxes fitted with properly 
marked terminals. The connecting cable between stations is then 
led to these terminal boxes, and connecting pieces are soldered to 
the wires of the cable and secured to the terminal contacts. An 
arrangement of desk telephone and terminal box is shown in Fig. 
3-47. 




Fig. 347. — Desk Phone with Cable and Connection Box. 



Navy Standard Telephones. 

Telephone instruments, switchboards and typical circuits as used 
on board our ships of war are dealt with in Chapter XXXIV, 
Electrical Interior Communications. 



CHAPTER XXXIV. 

ELECTRICAL INTERIOR COMMUNICATIONS. 

The conductors used with instruments and all means of interior 
communication devices are installed in conduit or molding which 
is in all respects like that described under Wiring Appliances. 

Wiring. 

Wire known as bell wire and interior-communication cable is 
used on all circuits, whether for generator or battery current, ex- 
cept where certain instruments require certain special cables. 
Interior-communication cable is used for all leads below the main 
deck, except for quarters and office calls in the non-water-tight 
system. In some cases this cable is used in non-water-tight sec- 
tions where the leads come through a bulkhead from a water-tight 
section. Interior-communication cable is used also for circuits to 
the conning tower, chart house, military top, signal towers, 
emergency cabins and bridge. 

All cables and wires for circuits used in action are kept below 
the water line as much as possible. Wires are run in conduit or 
molding with no more than 20 wires in any one lead. 

To avoid splices and joints, connection boxes for 20 or 40 wires 
are used where most suitable. In these boxes the wires are clamped 
to terminals, affording a ready means of testing any line or branch. 

Circuits used in action which are protected and which are con- 
nected to exposed circuits are provided with action cut-out switches 
for cutting out the exposed circuits. 

All leads into wiring appliances are made thoroughly water-tight. 

All wire and cable through decks or bulkheads, when molding is 
used, are led through standard stuffing tubes and when running 
through beams or bulkheads where water-tightness is not required, 
the hole for the lead is bushed with hard rubber. 



Electrical Interior Communication 763 

Where wires are connected through gaskets in boxes, cut-outs or 
instruments, the outer braid and tape on the ends of the wire is 
removed, exposing the vulcanized rubber, which should never be cut 
into or injured. 

When it is necessary to make joints in single conductor circuits 
it is done by first cleaning the wires, then twisting them closely 
together and heating sufficiently to cause the solder to flow freely 
into the joint. The solder used for making joints is of rosin-core 
type and no other flux than rosin used. All joints are taped while 
warm with a layer of rubber tape and covered with an outside layer 
of cotton tape. 

"Where several wires lead through tubes where water-tightness 
is required, the interstices are filled with rubber tape rolled spirally, 
especially those in the outer layer, and the whole is then wrapped 
with rubber tape, wrapped half its width, to completely cover the 
fillers, and increased at the gasket end to make it bind the wires 
tightly in the stuffing tube. 

Conductors for Interior-Communication Circuits. 

All conductors used with instruments or devices for interior com- 
munication are divided into two general classes, bell wire and cable. 
Bell wire is classed as 

a. Bell wire. 

b. Bell cord. 

Bell Wire. 
Bell wire is constructed as follows : 

1. A copper conductor consisting of one B. & S. G. Xo. 16 tinned 
annealed copper wire. 

2. A layer of vulcanized rubber. 

3. A close braid of Xo. 40 2 -ply cotton thread, braided with three 
ends. 

Bell Cord. — This is classed as bell cord, double, and bell cord, 
triple. Each conductor is constructed as follows: 

Each conductor is constructed as specified for double conductor, 
silk, in Chapter XXYI and two or three conductors thus con- 
structed are twisted together to form the bell cord either double 
or triple. 



764 Naval Electricians' Text Book 

Cable. 

Cable is classed as follows : 

a. Controller cable. 

b. Interior-communication cable. 

c. Battle-order cable. 

d. Bange-indicator cable. 

e. Powder-division cable. 

f. Night-signal cable. 

Note. — Cable classed in the above list as a, c, d, and e is not now 
standard, but will be found on many vessels. 

Controller Cable. — Each conductor is constructed as follows: 

1. A copper conductor consisting of nineteen No. 22 B. & S. Gr. 
tinned annealed pure copper wires, concentrically stranded. 

2. A layer of pure Para rubber taped or rolled on to a thickness 
of ■£% inch. 

3. A layer of vulcanized rubber to an external diameter of ^ 
inch. 

Seven conductors so constructed are laid up or twisted together 
to a circular section, six conductors lying around the seventh, and 
the wdiole is then covered with : 

1. A layer of vulcanized rubber to a diameter of fj inch. 

2. A layer of commercial cotton tape about -gj inch in thickness. 

3. A close braid of No. 30 3 -ply linen gilling thread braided with 
three ends. 

4. A close braid of No. 30 3-ply linen gilling thread braided 
wdth four ends, to a finished diameter of 1^ inch. 

This cable must show an insulation resistance between conductors 
and from each conductor to ground of not less than 1 megohm, 25 
feet, after immersion in sea water at a temperature of 72° F. for 
a period of twenty-four hours. 

Interior-Communication Cable. — Each unit conductor consists of 
seven No. 24 B. & S. G. wires, the seven grouped to approach cir- 
cularity of section, the whole wrapped with No. 80 cotton thread to 
a diameter of 0.068 inch, then covered with vulcanized-rubber com- 
pound to a diameter of 0.136 inch, then braided with No. 60 white 



Electrical Interior Communication 



765 



cotton thread, braided with three ends, the over-all diameter 0.156 
inch. 

The requisite number of unit conductors is laid up with a twist 
(having been filled with jute laterals to approach circularity of 
section), then covered with: 

(a) A layer of cotton tape. 

(b) A layer of vulcanized rubber. 

(c) A close braid of No. 20 2-ply cotton thread, braided with 
three ends, for all cables of less than twelve conductors, and of No. 
16 3-ply cotton thread, braided with four ends, for all cables of 
and above twelve conductors. 

(d) One unit conductor in each cable of and under seven wires, 
and one wire in the inner and one in the outer layer in each cable 
in excess of seven wires have three adjacent black threads woven in 
the white braid. 

Dimensions of standard interior-communication cable : 



Conduc- 
tors. 


Number of wires. 


Diameter in 
inches. 


Diameter in 32ds 
of an inch. 


1st 

layer or 

core. 


2d 
layer. 


3d 
layer. 


4th 

layer. 


Over 
conduc- 
tor. 


Over 
tape. 


Over vul- 
canized 
rubber. 


Over 
braid. 


3 
4 
5 


3 
4 
5 

6 
1 
1 
1 
1 
2 
3 
3 
4 
4 
5 
5 
6 
1 
1 
1 
1 
1 
2 
3 
4 
4 
4 
6 
1 
1 










.3987 

.4395 

.4841 

.5312 

.5312 

.5785 

.6350 

.6750 

.6875 

.7112 

.7235 

.7520 

.7729 

.7966 

.8220 

.8430 

.8430 

.8800 

.8910 

.9325 

.9875 

1.0000 

1.0360 

1.0645 

1.0854 

1.1345 

1.1562 

1.19125 

1.2035 


17 

18 
20 
21 
21 
22 
25 
26 
26 
27 
28 
29 
30 
31 
31 
32 
32 
33 
33 
35 
37 
38 
39 
40 
41 
42 
43 
44 
45 


19 










20 










22 


6 










23 




6 
7 
8 
9 
9 
9 

10 

10 

11 

11 

. 12 

12 

6 

6 

7 

8 

8 

9 

10 

10 

11 

12 

12 

6 

7 








23 


8 
9 








24 








27 


10 








28 


11 








28 


12 








29 


13 








30 


14 








31 


15 








32 


16 








33 


17 








33 


18 








34 


19 


12 
13 
13 

13 
15 
15 
15 
16 
17 
18 
18 
12 
13 






34 


20 






35 


21 
22 






35 
37 


24 






39 


26 






40 


28 






41 


30 






42 


32 






43 


34 






44 


36 






45 


38 


19 
19 




46 


40 




47 










766 Naval Electricians' Text Book 

Unit Conductors (Stranded). 



Wire. 


CM. 


Diameter in inches. 


B. &S. 


Number of 
strands. 


Over 
copper. 


Over 

cotton 

wrapping. 


Over 

vulcanized 

rubber. 


Over braid. 


24 


7 


2,828 


.060 


.068 


.136 


.156 



Battle-Order, Range-Indicator, Powder-Division Cables. — Battle- 
order cable consists of an insulated stranded conductor of 38,912 
circular mils cross-section, surrounded by 25 insulated conductors, 
each consisting of a single strand. 

Eange-indicator cable consists of an insulated stranded con- 
ductor of 22,799 circular mils, surrounded by 18 insulated conduc- 
tors, each consisting of a single strand. 

Powder-division cable consists of an insulated stranded conductor 
of 9016 circular mils, surrounded by 8 insulated conductors, each, 
consisting of a single strand. 

Each wire is thoroughly and evenly tinned. 

The stranded inner conductor of each cable is insulated as 
follows : 

1. A layer of pure Para rubber taped or rolled on to a thickness 
of not less than -g^ inch. 

2. A layer of vulcanized rubber as per table. 

3. A layer of commercial cotton tape, lapped to a thickness of 
T2 incn - 

The outer conductor of each cable consists of a No. 16 B. & S. G., 
insulated as follows : 

1. A layer of pure Para rubber taped or rolled on to a thickness 
of -^-inch. 

2. A layer of vulcanized rubber. 

In cables where the outer conductors are grouped in one layer, 
they are laid up with a left-hand twist, and when grouped in more 
than one layer, the layers are twisted in opposite directions, the 
innermost being left-handed. 

One conductor in each layer is braided with No. 60 white cotton 
thread. 



Electrical Interior Communication 767 

The outer layer of conductors is covered as follows : 

1. A layer of commercial cotton tape lapped to a thickness of 

A incn - 

2. A layer of vulcanized rubber as per table. 

3. A layer of commercial cotton tape lapped to a thickness of 

A incn - 

4. A close braid braided with four ends. 

Tests. — All the tests given in Chapter XXYI on Wires are ap- 
plied to Standard Bell Wire, Bell Cord, Interior-Communication 
Cable and Night-Signal Cable. 

The requirements of insulation resistance and high potential 
tests are given in the following table : 

Insulation resistance. %jff*£ 

Bell wire 500 megohms per 1000 feet. . 1500 

Bell cord No test 5000 

Cable. 
Interior-communication cable: 

Between conductors 1000 megohms per 1000 feet.. 1500 

Each conductor to ground.. 1000 megohms per 1000 feet.. 3500 
Night-signal cable: 

Conductor for 1000 megohms per length 3500 

Completed cable — 

Between conductors ...1000 megohms per 1000 feet.. 3500 
Cable to ground 50 megohms per length 3500 

Night-Signal Cable. — This cable consists of sixteen conductors 
made up as follows : 

Each conductor is made up of nineteen strands of No. 25 B. & 
S. G-. wire. 

The insulation is as follows : 

1. A layer of Para rubber -^ inch, rolled on. 

2. A layer of vulcanized rubber. 

3. A layer of cotton tape -g^inch thick. 

4. A close braid of No. 30 3-ply linen thread braided with two 
ends. 

Sixteen conductors so constructed are laid up in the finished cable. 

The cable is constructed as follows : 

1. The heart of the cable consists of a continuous length of 9- 



7G8 Naval Electricians' Text Book 

thread, tarred, well-stretched hemp rope, the upper end of the heart 
extending beyond the end of the cable conductors and finished with 
a neat, strong eye splice 3 inches in length. 

2. Around the heart are laid five of the unit conductors with a 
spiral lay and left-hand twist, and of a pitch to closely assemble 
the conductors on the heart. 

3. On the inner lay is laid the remaining eleven unit conductors, 
with a spiral lay and right twist, and of a pitch to closely assemble 
the conductors on the inner lay. 

4. The conductors are branched out for the lamps in pairs, using 
adjacent conductors and the reduction caused by the branching is 
made a neat taper by filling in with dead wire or jute. The branch- 
ing is first done from the outside layer and are spaced 12 feet dis- 
tance between lantern centers. 

5. The outer layer of conductors is securely hitched with marline 
hitches, 1 inch apart, using a 6-ply flax twine of about -J inch. 

6. The keyboard end of the cable is fitted with a standard male 
coupling. 

General Means of Interior Communication. 

The general means of interior communication controlled by elec- 
tric currents are divided into the following classes : 

1. Call-bell circuits. 

2. Telephone circuits. 

3. Telegraph circuits. 

a. Engine. 

b. Helm. 

4. Indicator circuits. 

a. Engine revolution. 

b. Helm. 

5. Fire-alarm circuits. 

6. General-alarm circuits. 

7. Warning-signal circuits. 

8. Battle and range-order circuits. 

9. Fire-control circuits. 



Electrical Interior Communication 769 

Call-Bell Circuits. 

The call-bell circuits comprise : 

a. Quarters and office calls. 

b. Voice-tube calls. 

The quarters call generally includes all calls for use of the com- 
mander-in-chief, the captain, wardroom officers and under this 
special calls, as for the executive, navigator, chief engineer, surgeon 
and marine officer; junior officers and warrant officers. 

Office calls usually include calls in the offices of the executive 
officer, navigator and paymaster, these being on the wardroom 
circuit. 

Voice-tube calls are installed at each voice tube, a return call 
being installed at each end of continuous tubes. 

Batteries for Quarters and Office Calls. — The circuits for quarters 
and office calls are divided into separate circuits ; thus all the calls 
for the use of the commander-in-chief are grouped on one battery, 
those for use of the wardroom on another and so on. The batteries 
are placed in battery lockers having a separate partition for each 
cell, the standard size inside measurement being 4f" X 4f ". There 
is a partition on the front of the cells to prevent their falling out 
when the door is opened. The door is provided with a snap catch 
and a name plate indicating the name of the circuit which the bat- 
tery supplies. 

Bell Work. 

For ordinary calls for attracting attention installed on shipboard, 
the electric bell or buzzer is commonly used, and the working of an 
electric bell requires a complete electric circuit from the source of 
current through the bell and back to the source. The circuits in a 
call system are composed entirely of insulated conductors, no part 
of the ship being used as part of the current path. In order that 
the call can be made at will and that the circuit shall be left open 
till needed it is necessary to introduce a switch in the circuit, this 
being accomplished by the ordinary push button. 

Typical Simple Bell Circuit. — A simple call-bell circuit is shown 
in Fig. 348. 



770 



Naval Electricians' Text Book 



T~} 



Fig. 348.— Bell Wiring. 



B is the battery, C the bell and P the push button. The action 
of an ordinary vibrating bell is so well known as to require no par- 
ticular mention. Closing the circuit 
by pressing P causes the circuit to 
be completed through the electro- 
magnet of the bell, in which the 
make and break of the current 
causes the hammer to vibrate, pro- 
ducing a continuous ringing as long 
as the circuit is closed. 
The object of the wiring of all bell circuits is to produce a definite 
result with the least expenditure of conductors, and a few examples 
of connection will be shown to illustrate the general principles. 

To Ring Two or More Bells in 
Different Places from One Button. 
— This may be accomplished by 
connecting all the bells in parallel 
from the mains containing the bat- 
tery and button, as shown in Fig. 
349. 

Pushing the button causes cur- 
rent to flow through all the 
branches containing the bells and each bell will have the same 
difference of potential at its terminals. 

Or, the bells, button and battery may all be connected in series 
as shown by Fig. 350, provided certain modifications are made in 

the bells. 

In this arrangement all but one 
bell must be changed to a single- 

T stroke bell, so that each impulse 

of current will produce only one 
movement of the hammer. The 
current is then interrupted by the 
vibrator of the remaining bell, the result being that all the bells 
will ring with full power. To cut out the circuit breakers on all 
but one bell it is only necessary to connect the ends of the magnet 
wires directly to the bell terminals. 




Fig. 349. — Bell Wiring. 



U 



:» O c D° O e 



Fig. 350.— Bell Wiring. 



Electrical Interior Communication 



771 



i_r 



To Ring One Bell from Two or More Places. — This may be accom- 
plished by placing the buttons in 
the different places in parallel 
with the mains containing the 
battery and bell, as shown in Fig. 
351. 

Pushing each button completes 

a circuit, so the same bell may be 

Fig. 351. — Bell Wiring. rung from widely different places. 



O 



y. 



Annunciator Systems. 

This is but an elaboration of the last examples of wiring, buttons 
being placed in widely different places which, when one is pressed, 
closes the circuit and rings a bell at some convenient point, at the 
same time, by a mechanical or electrical device, indicating the 
location of the button. 

A typical annunciator system is shown in Fig. 352. 

In this, one side of each button 
is connected to a battery wire b 
and the other to a separate lead- 
ing wire I, in communication 
with the drop on the annunciator 
corresponding to the button. 
There must be one wire from each 
button to the annunciator, but 
the other side may be connected 
to a common battery wire or to 
a common return, and it is in 
the connection to the common re- 
turn where the saving in copper 
arises. 

It is sometimes the practice, however, to run call mains through- 
out the length of the ship, especially if it be a small one, and from 
these mains are taken off different circuits as may be necessary; 
single-bell circuits, annunciator circuits, alarm circuits, etc. The 
following figure represents such an arrangement, being an example 
actually installed in a small vessel. 




Fig. 352. — Annunciator Wiring. 



772 



Naval Electricians' Text Book 



a and b (Fig. 353) represent the terminals of a double-pole 
double-throw switch, by which current for the mains is taken, 




Fig. 353. — General Interior Wiring. 



either from the generator mains T and T' or from the battery B. 
R is a resistance introduced in the generator circuit to reduce the 
E. M. F. of the generator to that of the battery. 1, 2 and 3 repre- 



Electrical Interior Communication 773 

sent push buttons on the upper deck, 1 connecting to the annuncia- 
tor A in the wardroom, 2 to a boat bell C in the wardroom and 3 
to an orderly's bell at D. Buttons 4 and 5 represent buttons in 
the wardroom state-rooms connected to the annunciator and 6 in a 
room to call the orderly at D. 

E, F, G and H represent alarm gongs connected in parallel be- 
tween the mains through the contact points, E, F, G, H. These 
gongs are partly electrical and partly mechanical, electricity only 
playing the part of setting the mechanical gear in operation by 
which the gongs are continuously rung till the spring actuating the 
mechanism is run down. Only a momentary current is needed in 
each gong, the energizing of an electromagnet starting the mechan- 
ism. There are three gong pushes represented at 7, 8 and 9, in 
each of which there are four contact points connected with E, F , G, 
and H. A small crank turns a switch connected at the center to one 
of the mains and it passes over the contact points. As it does so it 
makes the circuit complete through each gong, so they are each 
independently energized and their mechanism started. All four 
gongs can thus be started from any one of the buttons 7, 8 or 9, 
which may be widely separated from each other. 

This figure is intended to show some of the ways of connecting 
up different circuits and in which ingenuity in saving wire is a 
prime factor. Of course, with the energized mains any number or 
kind of circuit may be taken off, the principle of which is illus- 
trated in these cases given. 

Annunciator Wiring. 

The general scheme adopted is shown in Fig. 354. 

E represents the battery: A, the annunciator; B, a bell; B' , a 
buzzer, and P, pushes. One battery wire, the positive (usually 
white cable) leads to the bells or buzzers; a section wire, as at 6, 
leads from the bell to its push button and from that by the negative 
wire, common return, to battery. In the annunciator, a section 
wire is connected to the spring contact of the electromagnet for 
the particular station, the other terminal of the electromagnet being 
connected to the wire leading from the annunciator to the bell. The 
circuit is complete then through battery, positive wire, bell, lead 



774 



Naval Electricians' Text Book 




through annunciator, section wire, push button, common return 
(negative) to battery. In this particular system, pushes 1, 2 and 3 
are in widely different places, 4 and 5 are in close proximity, needing 

but one drop on the annun- 
ciator, hence but one section 
wire; 5 and 6 are in the 
same place, 5 going to the 
annunciator and 6 to a sepa- 
rate buzzer. This wiring 
illustrates the saving of cop- 
per leads, as one wire to the 
common return from 5 and 
6 is all that is necessary, 
and the common return may 
be a long distance away. 

Another annunciator sys- 
tem could be installed be- 
tween the + and — leads, 
the wiring in all respects be- 
ing the same as in the above. 
The section wires may enter many connection boxes in their leads 
and terminals are soldered to the ends stamped with the letter show- 
ing the circuit to which each section belongs and a serial number 
designating the particular station to which it leads. This leads to 
a ready means of recognition for purposes of testing or repair. 

Batteries Used with Bells and Buzzers. 

For a non-water-tight buzzer without annunciator, about five 
Leclanche cells in series are required. 

For the same with annunciator, about eight are required. 

For a water-tight bell and buzzer without annunciator, about 
eight cells. 

For the same with annunciator, 10 to 12 cells. 

Call Bells, Buzzers and Annunciators. 

Call bells and buzzers are of two general classes, water-tight and 
non-water-tight. Those of the water-tight type are of standard, 
navy type, the non-water-tight simply good commercial types. 



Fig. 354. — Annunciator Wiring. 



Electrical Interior Communication 775 

The water-tight bell consists of a yoked horseshoe magnet 
mounted in a water-tight composition box, the pole piece screwing 
into the magnet core through the outside of the box and made 
water-tight by lead washers. The armature is mounted on the out- 
side of the box and is pivoted at one end. The other end carries a 
stud which strikes a mica diaphragm on the side of the box when 
the armature is attracted. This stud strikes a plunger inside which 
actuates a make and break contact. 

The armature is protected by a non-water-tight cover. The leads 
are brought into the box through a stuffing tube and gland in one 
corner of the box. The magnet box is made water-tight by a cover 
screwing down on a rubber gasket. The bell is carried on an exten- 
sion of the box. 

The water-tight buzzer is in all respects the same as the bell 
with the exception that the bell extension, the bell and bell striker 
are omitted. 

Annunciators. — These are of three types : the non-water-tight and 
water-tight annunciators for call-bell and telephone systems and a 
special design of water-tight annunciator used in the fire-alarm 
system. All are of the gravity-shutter drop type, so designed to 
prevent the shutter from being dropped by vibrations or gun fire. 
The annunciator consists of a system of magnets and drops mounted 
in a water-tight composition box. The box is hinged in two places, 
the front "door opening to expose the magnets and the rear one open- 
ing to expose the contact springs to which the section leads are 
secured. The annunciator is wired through stuffing-boxes when 
molding is used and tapping in conduit when that is used. 

There is a separate electromagnet for each drop, being single 
pole, fastened to a zinc plate. When a magnet is energized it at- 
tracts its armature, which releases a shutter, this dropping by its 
own weight. On the shutter is marked the station from which the 
button is pressed. 

All section wires are connected to metallic springs in the rear 
of box. From each spring, contact is made to one terminal of the 
magnet through a screw passing through the zinc plate and insu- 
lated therefrom. The other terminal of the magnet is secured to a 
screw in the zinc plate which forms part of the common return. 



776 Naval Electricians' Text Book 

The non-water-tight annunciator is similar in its construction 
to the water-tight type, but is mounted in a wooden case. This 
type has only one door, for the purpose of examining the contact 
springs and connections. To get at the magnets it is necessary to 
unscrew the glass front. 

The fire-alarm annunciator is similar to that used with the call- 
bell system, but with the following exceptions : 

Below the drops are arranged a set of switches, one being in the 
section lead to each magnet. These are normally kept closed, but 
when the circuit through any magnet is established it should be cut 
out to prevent the continuous ringing of the bell. Both terminals 
of the magnets are insulated from the zinc plate, one being con- 
nected as before, the other to one side of the switch, and the other 
side of the switch connected to the zinc plate which forms part of 
the common return. 

Faults on Annunciator Systems. — Annunciators are made so that 
the front may be opened, exposing the electromagnets without dis- 
connecting any of the wires. Tre faults most likely to occur are 
grounds or leaks caused by moisture in connection boxes or by cor- 
roded contacts. The annunciator should first be tested, then the 
push buttons and then line. The annunciator is tested by the mag- 
neto for leaks between the terminal of the wire leading from the 
bell and the different section spring contacts. If a leak is found in 
a section, the push button should be examined, and if that is all' 
right, the line should be examined in all the connection boxes. 

The whole circuit can be tested for leaks by opening the battery 
switch and testing across the line terminals with a magneto, and for 
a ground, test from each terminal to earth. If a ground is dis- 
covered at the battery terminals, leave the switch open and test the 
annunciator between all the terminals and earth. If not found in 
first annunciator, leave it open and test the next, and so on. If the 
ground is not found in any of the section wires, then look for it on 
the battery wire leading to the bells in the connection boxes. 

An annunciator bell may not ring owing to weak current, in 
which case the battery should be examined and tested at its termi- 
nals for voltage. 

The dropping device in the annunciator may fail to work owing 



Electrical Interior Communication 



777 



to the contact maker of the bell being so adjusted that the vibra- 
tion is too rapid, so that the magnet does not have time., to act. 
This can be remedied by the tension spring. The springs of the 
armature clips sometimes become weak, either not allowing the shut- 
ter to drop or not holding the shutter in place. 

If any moisture makes its appearance in the annunciators, it 
should be at once dried out. This sometimes shows on the interior 
of the face. 

Telephone Circuits. 

Several types of telephone instruments have been designed to 
meet the requirements of ship installation, and a few of the types 
in most general use will be considered. 




Fig. 355. — Telephone Transmitter. 



Fig. 355 shows the details of one of the earlier forms of trans- 
mitters, a is a diaphragm of aluminum connected by the stem and 
nut c to the brass plate b, with base of mica set in brass box d. 
This box is filled with German silver filings. The brass box d is 
connected to the metal disc e by means of the stem / and support g. 
This metal disc is screwed to the wood of the telephone box. The 
flat springs s, s press with soft rubber feet against the diaphragm a, 
preventing any vibration in it except that caused by the voice. 

Current from the talking battery enters the contact piece I 
through the automatic switch in the telephone box, then by the 



778 



Naval Electricians' Text Book 



wire w to the stem c, through the German silver filings to the metal 
disc e and out by the contact piece m to a terminal on the bottom 
of the box, then through the receiver back to another terminal on 
bottom of the box and thence to the other pole of the talking battery. 
A receiver is shown in Fig. 356. The mechanism is encased in 
a rubber shell S, the upper part being cut away to allow the ear 
to be placed near the vibrating diaphragm. Inside there is a per- 
manent magnet P, of a shape like the figure 6, and on the inner 
curl is a projection C, forming the core of an electromagnet whose 
coil is in series with the transmitter through the wires I, I. Over 
the core C is a thin iron disc or diaphragm D, that is attracted 
more or less strongly by the current in the electromagnet. 




Fig. 356. — Telephone Receiver. 



The receiver has a hook, Ji, by which it is hung to the automatic 
switch, breaking the talking circuit, and a cord m secured to the 
base of the telephone box, by which its weight is taken from the 
connecting wires I, I. 

Cory Telephone Transmitter. — A type of transmitter extensively 
used, made by Cory & Son of New York, is shown in Fig. 357. 

The figure shows a metal casing which forms a chamber for the 
microphone and damper springs which are diametrically opposite 
each other and insulated from the case. The diaphragm is alumi- 
num and is attached to the upper electrode of the microphone and 
is pressed against a raised portion of the inner side of the circular 
disc which forms the top casing of the transmitter. Inserted be- 
tween the top and body of the casing and over the diaphragm is a 
resilient water-proof material which excludes all moisture. 

The lower electrode is attached to a screw which extends through 
the bottom of the casing and through a socket which is insulated 



Electrical Ixterior Communication 



79 



from the casing. A tapered thread on the outside of the socket 
with a nut is fitted for the purpose of locking the screw after the 
adjustment of the electrodes has been properly made. This adjust- 
ment is made with a screw-driver which may be used in a slot in 
the end of the screw. 

The space between the electrodes is about two-thirds filled with 
hard carbon granules. A soft felt ring encircles the electrodes for 
the purpose of holding the carbon granules in the space between 
the electrodes. 




Fig. 357. — Cory Transmitter. 



Electrical connection from the top electrode is made through the 
diaphragm and damper springs to a terminal in the bottom of the 
casing, and from the lower electrode to the socket around the screw 
to a similar terminal. These terminals are insulated from the case. 

Receiver. — Fig. 358 shows a cross-sectional view of the receiver 
used' with the transmitter described above. An annular metal case 
forms the chamber for the permanent and electromagnets and its 
top edge forms the lower bearing for the diaphragm. This is of 
sheet tin and is clamped between the case and the disc which forms 
the case cover. 

The permanent magnets are compound C-shaped and are two in 
number, with the open end of the C towards the center of the case. 
Screwed to them are soft-iron extension pole pieces. The cores 
for the electromagnets, two in number, extend through the pole 



780 



Naval Electricians' Text Book 



extensions and through the bottom of the case where they are 
secured by a jam-nut. The lower ends are slotted so that the dis- 
tance between the diaphragm and the core pieces may be adjusted 
by screwing them in or out without disturbing the magnet spools 
which fit over them. 

The above-described transmitter and receiver are used in two 
types of instruments, one a water-tight type, the other a non-water- 
tight type. 

Water-Tight Type A-l. — The particular characteristics of this 
type are shown in Fig. 359. There is a mouth piece which directs 
the sound waves to the transmitter in the center of the water-tight 
case containing all the working mechanism. In the inoperative 




Fig. 358. — Cory Receiver. 



position the opening to the transmitter is covered and made water- 
tight by an annular surface, which is held tightly against the base 
of the mouth piece by the tension of springs acting through arms, 
which are secured to discs on the ends of the cylindrical surface. 

There are two ear pieces, one on each side of the case, connected 
by flexible tubing to a tee piece which is in communication with the 
receiver mounted at the extreme top of the case. 

The connecting wires, three in number, are lead through conduit 
in the bottom and are connected to contact strips insulated from 
the case, along the inside of the back face. The connections 
through contact make and break switches, shown in the upper right- 
hand corner are such that when the ear pieces are hanging down 
and sprung into recesses on the outside of the case, the bell on the 
outside is connected to the calling circuit. To answer a call, the 




Fig. 359. — Water-Tight Type A-l Cory Telephone. 



782 



Naval Electricians' Text Book 



ear pieces are sprung from the recess and are raised, this operation 
having the effect of breaking the bell connections and connecting 
the receiver and transmitter to the line. This motion also turns 
the annular ring spoken of above, and brings an open space in it 
opposite the hole in the bottom of the mouth piece, and allows the 
sound waves to reach the transmitter. The transmitter itself is 
turned at the same time, the effect of which is to cause a motion of 
the carbon granules and prevents their hardening or packing. This 
turning effect is produced by the bell-crank arm and link shown in 
the figure. 

Connection to the transmitter is made through spring contacts 
from the main contact strips to projections on the trunnions of the 
movable discs which revolve the transmitter. This is frictional 
contact and allows connection while still allowing free movement of 
the transmitter. 

The contact strips are four in number though there are but three 

wires for each instrument. One strip 
forms the neutral wire terminal and is 
permanently electrically connected both 
to the transmitter and the receiver. 
One is connected to the bell through a 
make-and-break switch when the re- 
ceiver arm is in the inoperative position. 
Another is similarly connected to the 
other terminal of the bell. When the 
receiver arm is up the bell connections 
are broken and the receiver and trans- 
mitter are connected to the line. These 
connections are illustrated in Fig. 360. 
Terminal 3 is permanently connected 
to both the transmitter T and receiver 
R; 1 is connected through the left-hand 
spring switch to the bell B and 2 is 
similarly connected. When the trans- 
mitter is revolved, the middle spring- 
contacts are thrown to the right and left breaking the bell connec- 
tions and connecting terminals 1 and 2 to the receiver and trans- 
mitter respectively. 



mtk 



r£— 1 



00 



Fig. 360.— Terminal 
Connections. 




IATTERY LINS 

•O TRANS. AND REC 



RECEIVER LINE 



Fig. 361.— Non-Water-Tight Telephone, Showing Rear View with Back 

Removed. 



'84 



Naval Electricians' Text Book 




\\\^\\^V\\\\\\^^^^ 



Fig. 362. — Section View of Type C-3, Cory Telephone. 



Electrical Interior Communication 785 

Non-Water-Tight Type B-l. — The transmitter and receiver of 
this type are similar to those already described, but are mounted in 
a non-water-tight mahogany case. A general interior view is given 
in Fig. 361, showing the receiver mounted on the upper half and 
the transmitter on the lower half of the case. The sectional view 
of the receiver shows the C-shaped permanent magnets described 
under the Eeceiver. Provision is made for revolving the trans- 
mitter to give a motion to the carbon granules, and the connections 
are such that when the transmitter is held in its normal position by 
two heavy springs, the talking circuit is cut out, and to become 
operative the transmitter must be turned either to the right or left. 
While still inoperative for talking, the calling circuit to the bell 
is complete, and turning the transmitter for talking breaks this 
circuit and throws in the talking circuit. This operation is exactly 
the same as previously described, though the actual connections are 
different, but may be seen from an inspection of the drawing in 
Fig. 360. 

The two left-hand lugs shown above and below the spring are 
electrically connected to the back of the transmitter and serve as 
one terminal for the transmitter, dependent on which direction it 
is turned. A spring contact presses against the adjusting screw 
on the back electrode of the microphone and forms the other 
terminal. 

Water-Tight Type C-3. — This type also made by Cory & Son 
presents the peculiarities of those previously described, and in its 
external appearance is similar to Water-Tight Type A-l. The 
transmitter is somewhat different and the details may be seen in 
Fig. 362. Eaising the left-hand ear piece has the effect of opening 
the mouth piece to the receiver which remains closed and water- 
tight when the ear piece is down in its normal position. The trans- 
mitter is turned by raising the left ear piece and it is provided with 
lugs on its outside periphery which actuate the spring contact pieces 
controlling the circuits. Fig. 360 shows how the bell circuit is 
complete when the arm is down and how the connection to the 
transmitter and receiver is made when the transmitter is turned. 

Non-Water-Tight Type F. — The characteristics of this type are 
shown in Fig. 363. The receiver is connected to a megaphone 



786 



Naval Electricians' Text Book 




Fig. 363.— Non-Water-Tight Type F, Cory Telephone. 



Electrical Interior Communication 787 

which entirely surrounds that of the transmitter. The transmit- 
ter is turned by the handle shown at the bottom through a toothed 
are Avhich engages a similar arc on the face of the transmitter 
during which the change of connections from the bell to the talking 
instruments is made. 

Gun-Head Set. 

The Standard Gun-Head Set, as made by the Holtzer-Cabot 
Electric Company, consists of two receivers, one for each ear and 
one transmitter. The receivers are mounted in a padded leather 
head piece so arranged as to fit tightly around the ears, front and 
back, with the receivers held slightly away from them. The leather 
head gear is held by two buckled straps over the head, one near the 
forehead and one over the crown, and by a strap passing under the 
chin. The connecting wires to the receivers are carried to a termi- 
nal piece which is secured on one shoulder, and from these ter- 
minals, flexible wires are lead to permanent terminals secured at a 
convenient place in the circuits of the fire-control system. 

The transmitter is permanently secured in front of the mouth 
on two steel wires which pass across the face and around the head 
over the receivers. The wires are fitted with adjusting screws to 
suit different-sized heads and the transmitter itself is capable of 
adjustment in the direction of the supporting wires. The connect- 
ing wires are lead to the same shoulder terminal piece that takes 
the wires from the receivers. 

Transmitter. — The construction of the transmitter is shown in 
section (right) and with the back casing removed (left) in Fig. 
364. The general principles of this transmitter will be understood 
from the construction of the "solid-back" transmitter described in 
Chapter XXXIII. It consists of an enameled aluminum casing 
secured by three small screws to the enameled aluminum front. 
Screwed into the front is the nickeled-brass mouth piece, which is 
covered at the bottom by wire gauge soldered to it. Besting on the 
interior of the front is the German silver diaphragm held by soft- 
rubber bands and two springs shown in the left-hand figure. 
These springs are of steel and are screwed at one end into projecting 
pieces of the bridge and the other ends are enclosed in flat rubber 
tubes which press against the diaphragm. 



788 Naval Electricians' Text Book 

Secured to the outer casing and extending diametrically across 
the interior is the white nickeled-composition bridge which forms 
the solid back for the transmitting devices and holds the terminals 
for the leading-in wires. Between the bridge and the diaphragm 
is the aluminum cup which contains the supports for the electrodes, 
the electrodes themselves and the carbon granules. The electrode 
supports are of brass and are fitted with screw spindles at their 
centers, one of which screws into the bushing in the center of the 
bridge, and the other passes through the center of the diaphragm 
where it is secured by a nut. The rear end of the cup is covered by 







THIS VIEW SHOWS 
BACK CASING REMOVED 




Fig. 364. — Transmitter. 

a mica diaphragm held in place by an aluminum clamping ring. 
The electrodes are of carbon between which in the cavity of the cup 
are placed the carbon granules. 

One electrode is connected by a thin copper strip to one of the 
terminals on the bridge and the other by a flat copper strip and a 
flexible connection to the other terminal. The leads are taken out 
through the middle of the back casing. These details are seen in 
the left-hand figure. 

Receiver. — The construction of the receiver is shown in Fig. 365. 
It consists of a hard-rubber case made in two parts, the back case 
and front case; the front screwing on the back and between them 
is secured the diaphragm. The front is hollowed out to form a 



Electrical Interior Communication 



'89 



recess to fit the ear. The back is lined with a nickeled-brass lining 
which contains the magnets. The magnet is a compound circular 
one formed of four pieces of soft steel bolted together, three of 
them forming little more than 270 degrees. There are two magnet 
coils mounted on soft-iron cores which are bolted to the ends of the 
magnets. The cores are mounted on zinc supports, and are bent 
up at right angles to the diaphragm and brought near the middle 
of the case. The cores are provided with both a metal and fiber 
washer and over them are slipped the coils of the magnets. 




Fig. 365. — Head-Set Receiver. 

Between the ends of the magnet is secured a hard-rubber termi- 
nal block held by screws to the outside casing, and to which are 
secured two screw terminals to which the leads from the magnet 
coils and to the line are brought. 



Switchboard. 

The general practice has been to control all telephone circuits 
from one general switchboard, though at present two general cir- 
cuits, independent of the fire-control system, are installed ; one for 
general use and one for the engine and fire-rooms. The general use 



LINE DROPS 
PLUGLESS SWITCHES 

\ 

NAME PLATES 




s 

1ES 


mm 


) • 














, OPERATOR 


1 


2 


3 


4 


5 


6 


7 


8 


9 


^ 


o 


o 


o 


o 


o 


o 


o 


o 


G 






















o 


o 














- 


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o 


o 




• 












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o 


o 










• 


• 


• 


• 






















o 


o 










• 






- 



CLEARING OUT DROPS 
PUSH EUTTONS 



TERMINAL BOX 



Fig. 366.— Telephone Switchboard. 



Electrical Interior Communication 791 

circuit embraces all telephones installed in officers' quarters, offices 
and all stations outside of the engine and fire-rooms. The tele- 
phones on each circuit are controlled from its own switchboard. 

The switchboard is constructed for a central energy system and 
three 'wires lead from each instrument to it. It is of the plugless, 
cordless type and so arranged that five separate conversations can 
be carried on at the same time. The elements of the standard 
board, made by Cory & Son, are shown in Fig. 366. The working 
mechanism is contained in a water-tight brass case fitted with a 
cover which is made water-tight by dogs. Mounted inside and 
hinged to the bottom is a shutter on which are mounted the plug- 
less switches, the annunciator-target drops, the clearing-out drops, 
push buttons for calling, name plates, and the operator's receiver 
and transmitter. The drawing shows connections to nine instru- 
ments arranged in five rows and for each extra station a separate 
vertical strip containing a line drop, name plate., switches and push 
button would be added. Two stations in any horizontal row can 
communicate, but neither one of these two in another row can be in 
communication with another station at the same time as the first. 
Thus 1 and 2 in the first row, 3 and 4 in the second, 5 and 6 in the 
third, 7 and 8 in the fourth can all be in communication at the 
same time, but 1 and 3 in the second row could not communicate 
at the same time, nor 2 and 4, etc. 

The line drops are of the self -restoring type, and the indication 
consists of three white panels showing on a normally black disc. 
As soon as current is cut off, they automatically restore and show as 
plain black discs. The clearing-out drops are of the same type as 
the line drops and give the same indication. When the horizontal 
row is clear, that is, when all telephones are in their inoperative 
positions, the discs show black, but as long as any instrument has 
not been returned to its normal position, the target shows three 
white panels on a black background. 

The push buttons are fitted one for each station for the purpose 
of allowing the operator to call up any station. 

Connection is made by the operator to any station or between 
any two stations by means of plugless switches operated by levers, 
which are moved either up or down, one up and one down. This 



792 Naval Electricians' Text Book 

breaks the calling circuit and throws in the talking circuit. The 
wires lead to a series of platinum-tipped contact springs, eighteen 
to each switch, and the contacts are closed or opened by the cam 
switches. 

Each vertical row of switches may be separately removed by 
taking out the screws holding the strip and pulling on the switch 
levers. 

A portion of the switchboard case is separated from the main 
body, shown at the bottom of the drawing, and forms a connection 
box for all the wire terminals leading from the telephones. The 
different circuits are carried in conduit which is tapped into the 
connection box, thus keeping it water-tight. The box is covered 
by a screwed top also for water-tightness. The terminals for the 
different circuits are mounted on micanite strips fastened longi- 
tudinally along the box. 

Talking Batteries. — Each horizontal row is provided with a 
separate battery, so that conversation may be carried on between 
two stations in each row. These batteries are of the Gonda type 
and are arranged six cells in each battery. A separate spare battery 
is provided for each row, and five double-pole, double-throw switches 
are provided on the interior-communication switchboard, so that 
either battery may be used on the switchboard. 

Ringing Battery. — On the interior-communication switchboard, 
there is a double-pole, double-throw switch, and on one side of the 
switch is provided a battery of twelve Gonda cells for furnishing 
the current required for ringing. The other side of the switch is 
connected to the intermediate voltage terminal of the dynamotor, 
and either source of current may be used at will. 

Wiring Diagram. — The wiring of the switchboard and instru- 
ments is illustrated in Fig. 367. This shows the wiring of the 
operator's telephone, 0, and two stations, A and B, for talking and 
one station, A, wired to show the calling circuits. It will be re- 
membered that there is a separate talking battery, TB, for each 
row of horizontal switches, and conversation can only be carried on 
between two stations in one horizontal row, and not with one in 
one row and one in another. For each telephone added to the 
system, there would be an additional vertical row of switches, with 
line drop, push button and name plate. 



Electrical Interior Communication 



793 



IB 



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H 



C.0.0. 





Ro 



To 



l>4 fat nso 



A 

o 




IS* 



I 



1 pii nzi 



I 



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CONNECTION OF CO-0. 



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P.B. 



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P.B 



10 



LJ 




sj \_s- ft 

R.B. 

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Fig. 367.— Wiring Diagram of Telephone Switchboard. 



794 



Naval Electricians' Text Book 



Plugless Switch. — There is a plugless switch for each telephone 
in each horizontal row ; thus, if there are forty telephones, including 
the operator's instruments, connected so that five conversations can 
take place simultaneously, there will be two hundred plugless 
switches. Each switch has eighteen platinum-tipped contacts, as 

shown in the wiring diagram, 
the light lines representing 
the contacts and the black 
lines the platinum tips. The 
double-tipped contact is mov- 
able.and can make contact to 
the "one either above or below 
it by operating the lever. 
When the switch lever in any 
row is inclined up, the bot- 
tom row of double-tipped 
contacts is pushed down, 
making connection with the 
lowest line of contacts, and 
when it is down, the upper 
row of double-tipped contacts 
is pushed up, making connec- 
tion with the highest line of 
contacts. It must be remem- 
bered that only either the up- 
per or lower line of contacts 
is connected to the circuit 
and not both, and that when 
connection is made between 
two stations, the switch lever at one station must be up and the one 
at the other, down. 

The details of the switch are shown in Fig. 368. Six contacts 
are shown ; the other two series of six are in line with them and are 
entirely similar. The three double-tipped contacts on either side 
of the switch lever are moved together and make connection with 
the three in either outer line. 

The general operation is as follows: Suppose station A wishes 







Fig. 368.— Plugless Switch. 



Electrical Interior Communication 795 

to communicate with station B. The one at telephone A revolves 
his transmitter, which throws current from the ringing battery 
RB or dynamo tor D on the line and the indication is shown on 
the line drop over A's name plate LB, showing three white bands 
on the black background. The operator at the switchboard on 
seeing this signal moves one switch lever in the vertical row under 
A's name plate, say, up and one in his own vertical row and in the 
same horizontal row as that for A, down. He then revolves his 
transmitter which connects his telephone with that of A and com- 
munication can be effected. At the same time current flows from 
the talking battery through the clearing-out drop COB for that 
particular horizontal row and gives the indication of three white 
bands on a black background and shows that that horizontal row is 
busy. 

IToving a switch in A's vertical row, either up or down, breaks 
the circuit of the ringing battery and the line drop restores itself 
to its original condition. 

On learning from A that station B is desired, the operator presses 
the push button PB in B's vertical row which closes the ringing 
circuit through the bell at B. At the same time, the operator 
moves his switch to its normal position and moves a switch in B's 
vertical row, and in the same horizontal row as A, in the opposite 
direction to that of A. This puts A and B in communication and 
the clearing drop shows that horizontal row is busy, while the opera- 
tor is free to communicate with another station through another 
horizontal row. 

When A and B are finished, they return their transmitters to the 
original position, when the clearing drop indicates " clear " by 
showing its normal indication, and the operator then moves the 
switches to their original positions. The drop indicates clear when 
both or either one of the telephones are in their inoperative posi- 
tions, and if one should be left connected to the line, the line drop 
will indicate it when the switch is returned to its normal position. 

Ringing Circuit. — Suppose central wishes to call station A. He 
does so by pressing the push button PB for that station, and the 
circuit can be traced as follows: Starting from one side of the 
dynamotor D or ringing battery RB through double-throw switch S 



796 Naval Electricians' Text Book 

to common wire 1, through wire 2 to contacts 3, 4, 5, 6, 7, 8, to 
terminal 9 on telephone A, to contact 10, through bell on A, to con- 
tact 11, to terminal 12, to contacts 13, 14, 15, 16, 17, 18, through 
push button to common wire 20 and to the other side of battery or 
dynamotor. 

If an out station as A wishes to call central, the circuit is thus 
traced : As before from the battery or dynamotor to terminal 9 on 
telephone A, which has been turned to call central, then to contact 
21, through receiver R A to terminal 22, through contacts 23, 24, 25, 
26, 27, 28, through line drop LD, through relay magnet R to com- 
mon wire 20, to battery or dynamotor. When current flows 
through the relay magnet R it attracts its armature which closes a 
local circuit containing a bell, current flowing direct from the bat- 
tery through the bell when the switch 8' is closed. This acts as a 
night bell to attract the attention of the operator, or may be left in 
to be used in connection with the drop. 

Talking Circuit. — Suppose the operator is connected to an out 
station B with the operator to talk to B, and that the operator's 
switch is down and B's switch is up. Current then flows from one 
side of the talking battery TB, through the clearing-out drop COD, 
to contact 29, to terminal 30 on the operator's telephone, through 
To, to contact 31, to terminal 32, contact 33, wire 34, contacts 35, 
36, to terminal 37 on B, to contact 61, through receiver R B to ter- 
minal 38, to contacts 39, 40, wire 41 to wire 42, to other side of 
battery. 

The circuit from B to the operator with same arrangement of 
switches is to terminal 30 on the operator's telephone as before, 
through R , to contact 43, to terminal 44, to contact 45, wire 46 
to contacts 47, 48, to terminal 49 on B, to contact 50, through T B , 
to terminal 38 and back to battery as before. 

With the switches reversed, that is, with operator's switch up and 
B's switch down, for the operator to talk to B, the circuit is : From 
battery through clearing-out drop to wire 51, to contact 52, to ter- 
minal 38 on B, through R B , to contact 61, to terminal 37, to con- 
tact 53, over wire 46, to contacts 54, 55, to terminal 32, to contact 
31, through T , to terminal 30, to contacts 56, 57, to wire 42, back 
to battery. 






Electrical Interior Communication 797 

The circuit from B to the operator with the same arrangement of 
switches is to terminal 38 on telephone B as before, then through 
T s to contact 50, to terminal 49, to contact 58, over wire 34 to 
contacts 59, 60, to terminal 44, to contact 43, through B , to ter- 
minal 30, to contacts 56, 57, to wire 42, back to battery. 

It will be noticed in the reversal of switches results in the cur- 
Tent flowing in opposite directions through the receivers and so 
changes their polarity, an effect which tends to increased efficiency 
of talking. 

Care and Management. — The trouble that is most likely to occur 
in the telephone system consists of grounds, caused by moisture 
finding its way to any part of the apparatus or conduits. Tests for 
open circuits and grounds should be made daily with the magneto 
at the battery switchboard for both ringing and talking circuits. 
This can be done by testing from one of the battery switches on the 
interior-communication switchboard with all the switch levers up, 
and if found clear, with all down. If a leak or ground is shown, 
the switches should be opened one at a time, until the fault disap- 
pears, and that particular circuit should be disconnected and the 
circuit further tested by disconnecting the wires at the telephone to 
see if it is in the instrument or in the line. If in the line, it must 
be traced through each connection box. 

The switchboard and interior of instruments should never be 
opened in search for troubles, until all other means have been tried. 

Batteries should be tested each day for voltage and should be 
kept charged to their full capacity. 

In operating the switches, they should not always be used in the 
same way, that is, not always up or always down, but should be 
interchanged, as this changes the direction of the current through 
the receiver, reversing the magnet polarity and improves the talking 
qualities. 

TELEGRAPH CIRCUITS. 

Engine Telegraphs. 

These are installed on the bridge, in the conning tower and cen- 
tral station and sometimes in the chart house with indicators in 
each engine-room. The indicators in the engine-rooms are some- 



793 Naval Electricians' Text Book 

times fitted with transmitters to return the given signal. Cut-out 
switches are used on the circuits to the bridge and chart house, so 
as to cut them out of circuit in time of action. 

These telegraphs are used to signal to the engine-rooms an in- 
creased or decreased number of revolutions, usually from one to 
four. The telegraphs are of the lamp pattern, the operation of 
moving a handle on the transmitter ringing a bell at the indicator 
to call attention and at the same time lighting a lamp which illumi- 
nates a number indicating the number of revolutions desired. 

The transmitter includes an indicator, both mounted in a cylin- 
drical case on a pedestal. The dials are divided into eight segments, 
four for increased revolutions and four for decreased. Each lamp 
is in a separate compartment, so that the illumination can only 
show on a single number. 

The calling circuit consists of an arrangement of magnetos and 
bells, there being a magneto at each transmitter and a bell at each 
indicator, and this circuit is entirely independent of the lamp 
circuits. The magneto bell at each indicator is wired in series with 
the magnetos at the transmitters, so the call is given at all indi- 
cators simultaneously. The armature of the magneto at a trans- 
mitting station is revolved by the action of the handle moving over 
the face of the dial, the motion being multiplied by sprocket chains 
operating gear wheels. 

The contact maker in the transmitter consists of two carbons, one 
of which is always in contact with the common return wire from the 
lamps. The other makes contact when moved by the handle with 
separate strips of metal, one for each lamp, which are connected to 
the section wires leading to each lamp. 

To send an order by the transmitter, the handle is moved all the 
way across the dial, this motion revolving the armature of the mag- 
neto, setting up an alternating current which rings the bells at all 
indicators. The pointer of the handle lever is left in the center of 
the division containing the required order and a clutch drops in a 
notch to hold it. This completes the lamp circuit through the 
lamp in the indicator of the transmitter and through each other 
indicator, illuminating the number which represents the desired 
order. 



Electrical Interior Commukication 799 

The indicators in the engine-rooms are similar in all respects to 
the indicators of the transmitters. 

The lamp circuit is on the generator potential, the whole circuit 
being protected by fuses and controlled by a switch usually located 
on the interior-communication switchboard. 

The wiring is all in standard interior-communication cable run in 
conduit, usual connection boxes being installed. 

Sources of Trouble. — The magneto circuit must be carefully 
watched for grounds, as they are liable to occur owing to the high 
E. M. F. of the alternating current, but these can be easily tested 
for in the terminals of the magneto in the pedestal of the trans- 
mitters. 

If a lamp fails to light, it may be due to a broken filament or a 
loose contact in the socket. 

The connection boxes are the most fruitful sources of grounds, 
and if any appear, these should be examined first for moisture or 
corroded contacts. 

Wiring. — The transmitters and indicators are all wired in mul- 
tiple from a generator circuit. A typical circuit is shown in Fig. 
369, where all corresponding wires are numbered to aid in tracing 
the leads and connections. 

Helm Telegraphs. 

These are located on the bridge, in the chart house, in the conning 
tower and in the central station. Eeceivers are provided in the 
tiller room, steering engine-room and at the after wheels. Cut-out 
switches are placed on the circuits leading to the bridge, chart house 
and after wheels. 

These telegraphs are used to signal different helm angles to the 
different steering stations. Combined transmitters and indicators 
are installed at all sending stations and receivers, or indicators, at 
each receiving station. 

The transmitters and indicators and the method of signaling is 
exactly the same as in the case of engine telegraphs, with the excep- 
tion that the dials are marked to show in degrees, there usually 
being four signals to each side, starboard and port. The dials are 
marked 0°, 5°, 15°, 35°, port, and steady, 5°, 15°, 35°, starboard. 



800 



Naval Electricians' Text Book 



The calling circuit is the same as for the engine-room telegraphs, 
and the method of wiring is in all respects like that circuit. The 



STAR ENCtNt ROQIA 



TO 
PORT INSTRUMENTS 



OYNAMO toAIMi 




C* ff 

TR ANaNUTI 



CONNING TOWtR. 
Fig. 369. — Wiring of Engine Telegraphs. 



current is taken from a generator circuit, properly switched and 
fused. 

The wiring shown in Fig. 369 illustrates the wiring of these in- 
struments, all the instruments being connected in multiple. 



™^™™i 



Electrical Interior Communication 801 

INDICATOR CIRCUITS. 
Engine-Revolution and Direction Indicators. 

These are intended to indicate the direction of the revolution of 
the main engines, and by means of a watch to tell the number of 
revolutions in any given time. 

They consist of transmitters and indicators, the transmitters in- 
stalled in the shaft passages, with indicators in the engine-rooms, 
conning tower, chart house, on the bridge and in the central station. 
Cut-out switches are installed on those circuits leading to the chart 
house and bridge. 

The indicator consists of a circular water-tight case with a glass 
front covered with a dial of white porcelain, marked u Ahead " 
and " Astern." Below these words are two small pointers which 
are given a motion of 45 degrees from the vertical by the control- 
ling mechanism. This motion is intermittent, one motion from the 
vertical and back corresponding to one revolution of the engine 
shaft. When the engine is going ahead, the pointer under the word 
" Ahead " is worked by the mechanism. The mechanism consists 
of two complete double-pole electromagnets, one for use with the 
" Ahead " pointer and one for the " Astern." The circuit is made 
and broken by the transmitter in the shaft passage, and the magnet 
is alternately magnetized and demagnetized, attracting an armature 
which actuates the pointer. 

On each shaft is secured a toothed-wheel eccentric with the shaft, 
engaging a smaller tooth wheel, which causes a small rod to move 
up and down, closing the circuit to the magnet once each revolution. 

On the base of the indicator dial is a switch by which the circuit 
can be thrown in when indications are desired, otherwise the circuit 
is completely off, though the transmitter is continually working. A 
lamp behind the dial serves to illuminate it when required. 

Wiring. — The wiring is in standard cable and connection boxes. 
The current is obtained from a battery of cells, ten to twelve cells 
being required for the indicator. The lamp terminals are connected 
to a generator circuit. 

The wiring plan is shown in Fig. 370. 



802 



Naval Electricians' Text Book 



Helm-Angle Indicators. 

These are intended to indicate the angle of helm, and consist of 
a transmitter located in the tiller-room and indicators in the steer- 
ing engine-room, conning tower, chart house, on the bridge, at the 
after wheels and in the central station. Cut-out switches are placed 
on the circuits leading to the chart house, bridge and after wheels. 

The indicator is of the lamp pattern and is of the same type as 
the indicator used in the engine and steering telegraphs, but it 

CONNING TOWER 

Star* 






CUT OUT 



LAMP 
MAINS 



l|l|l|l|l|l|l|l|l|H 

Fig. 370. — Wiring of Revolution Indicators. 



contains fifteen lights instead of eight. The starboard side of the 
indicator shows green lights and the port side, red, the 0°, or amid- 
ships position, showing white. The dial is marked on each side 
2 J, 5, 7i, 10, 15, 25, 35, these representing the number of degrees 
the helm makes with the fore-and-aft line. 

The transmitter consists of an arc of about 80 degrees, on which 
are mounted strips, one for each of the number of degrees indi- 
cated, and these are all insulated one from the other. Concentric 
with this arc is another solid strip, to which the common return 
wire is secured. These two arcs are mounted near the rudder head 



Electrical Interior Communication 



803 



and the contact maker consists of a brass arm carried by the rudder 
head, the arm resting on both arms, putting the section in circuit on 
which it rests. Putting any section in circuit lights a lamp in each 

conning tower 




MAINS PORT 




INOiC ATOR 




STAR. 



ro 
CENTRA L 
STATION 

A ISO 

PH. 



Fig. 371. — Wiring of Helm-Angle Indicators. 



indicator showing the angle of helm by illuminating a number cor- 
responding to that section. 

The wiring is similar to that of engine and steering telegraphs. 



804 Naval Electricians' Text Book 

Interior-communication cable is used, and wired with conduit and 
connection boxes. 

The current is on the generator potential, being controlled by a 
properly-fused switch in central station or dynamo-room. All 
indicators are wired in multiple, as shown by Fig. 371. 

Fire-Alarm Circuit. 

The wiring of the fire-alarm or thermostat circuits is similar to 
that of annunciator circuits, one battery wire being led to all 
thermostats as a common return, a separate section wire running 
from the thermostat to the annunciator. When two or more 
thermostats are in the same compartment, they are wired in parallel. 

The thermostats are placed in metal cases overhead in certain 
store-rooms and overhead and on bulkheads in coal bunkers. In 
some cases there is a separate circuit for fire alarms in magazines. 
These circuits are supplied by a battery of cells, twelve being usually 
sufficient. The annunciator is generally installed near the cabin, 
under care of the orderly, but later practice installs it in the 
dynamo-room. 

Thermostats. — Thermostats are devices installed for the purpose 
of giving warning in case the temperature of the air in the neigh- 
borhood of their location rises above a certain degree. They are 
wired in open electrical circuits in such a manner that any increase 
of temperature above a specified amount acts to cause them to close 
the circuit which is connected with the alarm bell. 

Two general types have been used, known as mercurial and me- 
chanical types. The mercurial type consists of a metallic cup filled 
with mercury and sealed with a plug made of paraffin paper. 
Through the center of this plug passes a small glass tube similar 
to the tube of a thermometer, with its lower end flush with the 
mercury. A platinum wire passes through this tube and is secured 
to a brass plate on the insulating plug. The metallic cup forms one 
pole and the brass plate the other to which the circuit wires are 
secured. 

As the temperature rises, the mercury expands from the cup up 
the tube, and at a certain temperature it makes contact with the 
platinum wire and closes the circuit through the annunciator and 



Electrical Interior Communication 805 

rings the bell ; at the same time dropping the shntter marked with, 
its location. The thermostat is mounted in a water-tight box which 
is tapped for the conduit carrying the circuit wires. A hole in the 
bottom of the box exposes the metal cup of the thermostat. 

The thermostat should be tested by the flame of an alcohol lamp, 
and this should be done with great care, as too much heat is liable 
to break it. Heat should be applied slowly, removing the lamp at 
intervals and taking it away entirely the instant the circuit is 
closed. There should be some arrangement of signals by which it 
is known the moment the bell rings on the annunciator. The cut- 
out switches on the annunciator should always be in circuit and- in 
testing they can be cut out when the bell rings but should be closed 
when the test is over. 

The mechanical thermostat depends on the expansion in length 
of a metal rod when it becomes heated. The active portion of the 
mechanical thermostat is a coiled spring, which, when heated with 
one end held fast, increases in length, and in so doing the free 
end turns. 

The coil is a right-hand composite steel and brass spring of 7-J 
turns, composed of steel inside, f inch wide and .014 inch thick 
and brass outside .034 inch thick brazed together. As a protection 
from corrosion the springs are well tinned. The top of the spring 
is free and to it is secured a brass contact arm, and as the free end 
of the coil moves it carries this contact arm and with sufficient in- 
crease in length due to heat, the arm moves far enough to bring up 
against a terminal to which the leading wire to the annunciator is 
secured. The lower end of the spring is held fast by being screwed 
into a spindle which runs up through the inside of the coil and 
secured to the casting by which the thermostat is bolted in place. 
The other leading wire is secured to a terminal on the casting and 
the circuit is completed through the coil. 

The terminal with which the bent arm on the free end of the 
spring makes contact is adjustable as to the distance the arm has to 
move to make contact by means of a set-screw and as the expansion 
depends on the temperature, this distance can be regulated for a 
given temperature. 

Thermostats differ in type according to their location. For bunk- 



806 Naval Electricians' Text Book 

ers the whole mechanism is enclosed in a water-tight case except 
sometimes when they are placed overhead when the spring may be 
protected by a perforated metal guard. For store-rooms the only 
protection necessary is that due to ordinary moisture and the greater 
area of the spring exposed to the heated air the better. The type 
for magazine is wholly enclosed so that the spark due to break of 
contact cannot come into direct contact with any inflammable gases 
that may be held in the magazine. 

General-Alarm Circuit. 

The general-alarm system consists of electromechanical, single- 
stroke gongs wired in multiple on a battery circuit and controlled 
by contact makers. The gongs are located in the living and work- 
ing spaces so as to be heard by all the ship's crew. The contact 
makers are located in the chart house, conning tower and state- 
rooms of the captain and executive officer, and are placed apart from 
all push buttons to prevent their being accidentally put in action. 

These gongs are partly electrical and partly mechanical in their 
action. Closing the circuit through one gong energizes an electro- 
magnet which attracts an armature, and the motion of this arma- 
ture sets in operation a clockwork mechanism which sets a striker 
in reciprocating motion, striking the gong by a series of single 
strokes. The magnet coils of the gong are thoroughly insulated 
from the cores, and the winding consists of cotton-covered copper 
wire, which is run through insulating varnish as it is wound on. 
This is to avoid the grounds so often found in these coils. The 
mechanical part of the apparatus is usually located at the gong, 
but may be combined with the contact maker. 

All the mechanism is inclosed in a composition-metal case, made 
water-tight by means of a sheet-rubber gasket. It has sufficient 
power to sound the gongs twice, two periods of not less than thirty 
seconds each, and after each action the mechanism returns auto- 
matically to its original state. 

Each electromagnet requires a difference of potential at its termi- 
nals of 15 to 20 volts. 

Contact Maker. — One form of contact maker used with these 
gongs consists of a brass water-tight box containing a hard-rubber 



Electrical Interior Communication 



807 



base on which are mounted section pieces separated from one 
another and to each of which is attached a section wire to each gong. 
Over these contact pieces slides a lever, pivoted at the center of the 
base, turned by a handle on the outside of the box, the common 
return wire to the battery connected to the lever at the center. 
From each gong is a common return to the battery. All the con- 







HOUSE 




OOOOe 




Fig. 372. — Wiring of General Alarm Gongs. 



tact makers are connected in parallel by branching all the section 
wires and common return to each contact maker. 

This system of wiring is shown in Fig. 352 and in Fig. 372. By 
this arrangement, as the contact lever is turned, successively making 
contact on each of the contact sections, the full battery current goes 
through each electromagnet. This system of wiring allows any 
single gong to be tested or rung from any contact switch and any 
fault to be easily found. 



808 Naval Electricians' Text Book 

Another form of contact maker used with single-stroke gongs is 
similar to the above, but requiring continuous turning of the handle 
over the contact sections, each gong getting the full battery power 
once in each revolution, giving one stroke of the gong. In this 
form, the gong is a purely single-stroke one and requires no me- 
chanical device at the gong, but only the electromagnet and arma- 
ture which forms the striker. 

To avoid turning the lever by hand, it is fitted with clockwork 
mechanism similar in its operation to that used with the " Warning 
Signals." The gear wheels of the mechanism are so proportioned 
that the contact maker makes about 20 revolutions for one turn of 
the operating handle, thus striking each one of the gojigs about 
twenty times. The speed of the revolution of the contact maker is 
controlled so as to allow time for each gong to operate and continue 
the sounding of the alarm for about 30 seconds. 

Care of Gongs. — In the electromechanical type, the armatures of 
the mechanism sometimes get out of adjustment, and this is reme- 
died by releasing the escapement several times, setting the adjust- 
ing screws to suit. Care must be taken that the springs actuating 
the mechanism are not wound too tight. 

Care must be taken that all contacts are kept clean and free from 
oxidation, and that in the rotary type of contact maker the tension 
on the contact spring is not too great, as too great friction between 
the switch and section points might cause the switch to stick, keep- 
ing the circuit closed through one of the gongs. 

The battery should be frequently examined to see that it keeps 
up full voltage. 

Warning Signals. 

These consist of shrill whistles, operated electrically from the 
chart house and other places, according to the class of vessel. They 
constitute the signal for closing the water-tight doors. Where leads 
go through the protective deck, they pass through action cut-out 
switches. 

The signal is required to be a succession of sharp, shrill whistles, 
audible above noise of running machinery, and differing in tone 
from any other whistle or signaling apparatus, so as to be instantly 
and unmistakably recognized under all conditions. 






Electrical Interior Communication 809 

In its ordinary form, its action is partly electrical and partly 
mechanical and presents no unusual principles. When circuit is 
established by a contact maker at the place designated, usually the 
chart house, current flows around an electromagnet in the whistling 
apparatus, which, when energized, attracts an iron plunger into its 
core, this plunger pulling down with it an air-tight chamber on 
which is mounted the whistle. The air having no escape, is forced 
through the whistle, emitting a shrill sound. When the circuit is 
broken by the contact maker, the air cylinder is in its lowest posi- 
tion, and it is forced up again by two strong spiral springs to its 
former position. The circuit is again closed by the contact maker 
and the operation is repeated, the reciprocating action lasting about 
35 seconds. 

The contact switch consists of a set of clockwork gear mounted 
in a brass water-tight case and actuated by a lever on the outside 
of the box. Eevolving the lever winds up a spring which sets the 
clockwork in motion and releases the lever, which falls back to its 
position by its own weight. 

On one side of the contact lever are two carbons which, when 
raised by the lever, make contact through two other carbons, to 
each of which one end of the line wires are connected. Besides the 
carbon contacts, there are metallic contacts, the carbon ones taking 
the spark in breaking the circuit, but on account of their high 
resistance not giving enough current to the solenoid. 

Great care is necessary in adjusting these contacts, allowing very 
little lead of the carbons, for otherwise the period of contact of the 
metal contacts is too short to allow of the reciprocation of the 
plunger of the solenoid. 

The contacts in the contact maker should be kept clean and 
bright and the springs of the plunger should have proper attention. 
If the plunger cylinder is not kept clean or is allowed to rust, it 
will not work freely in the outer cylinder. Grounds will most likely 
be found in the coils of the magnet and they can be located by 
removing the fuses and testing with the magneto. 

A typical circuit showing the method of wiring the controlling 
magnets is shown in Fig. 373. 

In this wiring, connection boxes are on the main leads ; branch 



810 



Naval Electricians' Text Book 



circuits taken to the whistles in parallel from the connection boxes. 
In some cases, two whistles are taken from the same branch, but 
there is usually but one. W represents the whistles, CB the con- 
nection boxes, DM the generator mains and 8 the controlling 
sivitch, usually located in the chart house. 



CB. 



O.M. 



rt 



CB 



®W 



Fig. 373. — Wiring of Warning Signals. 



Battle and Range-Order Circuits. 

Battle and range-order instruments consist of combined trans- 
mitters and indicators for battle orders, for range orders, for 
powder-division or ammunition-hoist orders and of receivers for 
battle orders, for range orders and for powder-division orders. 

These circuits are being replaced by the more modern fire-control 
circuits. 

The combined transmitter and indicator for battle and range 
orders consist of a rectangular metal box, water-tight and fitted 
with water-tight cover screwed on a rubber gasket. It is mounted 
on a pedestal through which the wires enter. In this transmitter 
are mounted two rows of 5-candle-power lamps and a series of snap 
knife-edge switches, one in the circuit of each lamp. The lamps 
are covered by a series of circular pieces of transparent plates on 
which are marked the necessary battle or range orders. Surround- 



Electrical Interior Communication 811 

ing each lamp is a metal tube, so all the light from one lamp will be 
thrown on its own plate and not illuminate any of the others. 

The switches are arranged in two rows one above and one below 
the lamps, the switch handles projecting through the cover and are 
so arranged that when the switch handle is horizontal, the switch 
controlled by it is open, and when vertical the switch is closed. 

The plates over the lamps are all contained in one piece which is 
secured by wing nuts and which may be readily removed, exposing 
the lamps. 

The receiver for battle and range orders consists of a rectangular- 
shaped metal water-tight case with hinged cover made water-tight 
by butterfly-winged nuts pressing it against a soft-rubber gasket. 
It is made to be secured against a bulkhead, the wires entering at 
the bottom through stuffing tubes. Inside the case are mounted 
four rows of lamps. The hinged cover is similar to that in the 
transmitter except that it is the same size as the receiver case, and 
has circular transparent discs with the orders marked on them cor- 
responding to those in the transmitter. The lamps are fitted with 
shades as in the transmitters. 

Wiring. — In the transmitter one terminal of each switch is con- 
nected to a common bus bar which forms a terminal for one of the 
generator wires, and the other terminal is connected to its section 
wire leading to its lamp. When the switch is turned the section 
wire is connected to the common return wire through the switch. 

In the receiver one terminal of each lamp is connected to a bus 
bar to which the common feed wire is connected. The other termi- 
nals are connected to the section wires leading to the switches in 
the transmitter. 

To transmit an order it is simply necessary to turn the switch in 
the transmitter for the lamp under the desired order, when that 
lamp in both the transmitter and receiver will be lighted. The 
wires used with these instruments are made up in cables, the section 
wires being formed around a central wire which forms the common 
return. The main feeders are protected by fuses of such capacity 
to allow generally four lamps in each transmitter and receiver to 
be lighted. 

If grounds appear, they will be indicated on the ground detector 



812 



Naval Electricians' Text Book 



on the main switchboard, and to locate grounds on any section wire, 
all the lamps in all receivers should be removed and each section 
tested separately. 

Powder-Division Circuit. 

The transmitter and receiver for this circuit are essentially the 
same as those for battle-order circuits and the wiring is on the 
same principle. The transmitter has one row of six lamps and one 
row of six switches mounted in a water-tight case on a pedestal, 
while the receiver has two rows of lamps of three each in a water- 
tight case designed to secure against a bulkhead. 



B.NA. 




(|) ® ® © © © 



Fig. 374. — Wiring of Powder-Division Circuit. 



The wiring for a typical powder-division circuit is shown in Fig. 
374, when T represents the transmitter, R the receiver, BM the 
battle mains and J a junction box. 

Fig. 375 represents the wiring of a typical circuit for battle or 
range orders. Current is taken from a battle main of the generator 
potential through a junction box to the transmitter where all the 
lights in the transmitter and in all indicators are controlled by 
switches. The wires from the transmitter to the different indica- 
tors are made up in one cable, that for the battle order consisting 
of one insulated stranded conductor of 38,912 circular mils sur- 
rounded by 25 insulated conductors, each consisting of a single 
strand. The cable for range-order instruments consists of an insu- 



Electrical Interior Communication 



813 



lated stranded conductor of 22,799 circular mils surrounded by 18 
insulated conductors, each consisting of a single strand. 

The cables may be led into connection boxes from which branches 
to separate indicators may be taken as shown in Fig. 375. T repre- 
sents the transmitter with switches S, R the receivers, CB a con- 
nection box, BM the battle mains and J a junction box. The cables 
are shown made up at C. 




Fig. 375. — Wiring of Range-Order Circuits. 



Fire-Control Circuits. 

The different electrical circuits under the present system of fire 
control are embraced under the following heads : 

1. Fire-control telephone system. 

2. Range and deflection circuits. 

3. Salvo-firing circuits. 

4. Broadside ammunition-hoist signals. 

5. Cease-firing circuits. 



814 



Naval Electricians' Text Book 



Fire-Control Telephone System. 

The object of this system of fire control is to afford direct com- 
munication from the different fire-control stations to the class of 
guns controlled from each station with intercommunication between 
certain of these stations. In general, there are two stations for the 
control of the 12-inch turret guns, one on each mast in a specially- 
constructed crow's nest. A short distance below these, or in the 
upper tops, are the stations for the control of the 8-inch turret guns. 
Other control stations are those for the broadside guns, both for- 
ward and aft on the starboard side and forward and aft on the 
port side; and for torpedo defense, both starboard and port, for- 
ward, and starboard and port, aft. 

In order to properly divide up the circuits with as little confusion 
as possible and that communication be rapid and direct, a series of 
sub-stations are provided with operators in each for the proper 
manipulation of the switches to put the desired stations in com- 
munication with each other, and for passing the word received from 
the fire-control stations to the divisional officers and gun-pointers. 

The following table shows the general distribution and installa- 
tion of telephones in a modern vessel. At each one of the stations 
designated by a serial number there is installed some form of a 
head set of telephone instruments, including double receivers and a 
transmitter : 







TELEPHONE 


STATIONS. 




d 
ft 
43 


d 
ft 


Location and leads from 


To 


d 
ft 




u 










'2 


1 
1 


1 

2 


Captain's battle station. 
Central station No. 1. 

Telephones 1 or 2 connects with 
3-4-6-6-7-8 or 9 by means of a trans- 
fer switch in panel in central sta- 
tion No. 1, and are connected to 
the same circuit. 


For'd 12" F. C. S. 

After 12" " 

Star. forM torp. def. F. C. S. 

Port " 

Star, after " li " 

Port " 

After torp. firing station. 


3 

4 
5 

6 

7 
8 
9 


2 


10 


For'd 12" F. C. S. 

Telephones 10-11-12-13 are all 
connected in parallel on the same 
circuit. 


Sub-station No. 1, Range. 
" Deflec. 
" B.o. 


11 
12 
13 


3 


14 


After 12" F. C. S. 

Telephones 14-15 16-17 are all 
connected in parallel on the same 
circuit. 


Sub-station No. 2, Range. 
" Deflec. 
" B.o. 


15 
16 
17 



Electrical Interior Communication 



815 



TELEPHONE STATIONS.— Conimwed. 



6 

'3 

o 


d 
[3 


Location and leads from 


To 


6 

■S 


5h 

5 


- 

02 






0> 
CO 


4 


18 


Sub-station No. 1. 


For'd 12" turret right sight-setter. 


19 






By means of transfer switches 


ii le(t 


20 






on panel in sub-stations 1 and 2, 


" " " trainer. 


21 






telephones 18 and 19-20-21-22-23 are 


" Turret Off. right. 


22 






connected in parallel on circuit 4 


ii i, i. » ii left> 


23 






or telephones 18 and 25-26-27 28-29 










are connected in parallel on the 










same circuit. 






5 


24 


Sub-station No. 2. 


After 12" turret right sight-setter. 


25 






By means of transfer switches 


" " " left 


26 






in sub- stations 1 and 2, telephones 


" " " trainer. 


27 






24 and 19 20-21-22-23, and 24 and 


" " " Turret Off. right. 


28 






25 26-27 28-29 are connected in 


ii i, ii » » left> 


29 






parallel on circuit No. 5. Both 










turret guns can be controlled 










from either sab-stations 1 or 2. 






6 30 


For'd 8'' F. C. S., star. 


Sub-station No. 3, Range. 


32 




31 


After 8" 


" Deflec. 


33 






Telephones 30 or 31 are connect- 


" B.o. 


34 






ed to 32-33-34 by a transfer switch 










in sub-station No. 3. 






7 


35 


For'd 8" F. C. S., port. 


Sub-station No. 4, Range. 


37 




36 


After 8" 


" Deflec. 


38 






Telephones 35 or 36 are connect- 


" B.o. 


39 






ed to 37-38-39 by a transfer switch 










in sub-station No. 4. 






8 


40 


Sub-station No. 3. 


For'd 8" turret right sight-setter. 


41 






The group of telephones in 


" " " left 


42 






each 8" turret is connected to a 


" " " Turret Off. right. 


43 






double-pole double-throw trans- 


ii i, „ » » left- 


44 






fer switch in sub-station No. 3, 


After 8" turret right sight-setter. 


45 






and by properly closing these 


" " " left 


46 






switches telephone 40 can con- 


" " " Turret Off. right. 
" " " " '• left. 


47 






nect with all the telephones in 


48 






any one group, or with all the 


Star. 8" turret right sight-setter. 


49 






telephones in all four groups. 


" " " left 

" " " trainer. 

" " " Turret Off. right. 

" " " " " left. 
Port 8" turret right'sight-setter. 
" " " left 


50 
51 
52 
53 
54 
55 






" " trainer. 


56 








., ii .. Turret Off. right. 


57 








i. i« .. i. ii left> 


53 


9 


59 


Sub-station No. 4. 

By the transfer switches in this 
station, telephone 59 can connect 
with all telephones with which 
No. 40 can connect. 






10 60 


For'd 6" F. C. S., star. 


Sub-station No. 5, Range. 


62 


61 


After 6'' 


" Deflec. 


63 






Telephones 60 or 61 connect with 


" B.o. 


64 






62 63 64 by a transfer switch in 










panel in sub-station No. 5. 






11 


65 


For'd 6" F. C. S., port. 


Sub- station No. 6, Range. 


67 




66 


After 6' 


" Deflec. 


68 






Telephones65 or 66 connect with 


" B.o. 


69 






67-58-69 by a transfer switch in 










sub-station No. 6. 







816 



Naval Electricians' Text Book 



TELEPHONE STATIONS.— Continued. 



Location and leads from 



To 



12 



13 



TO 



14 



15 



16 



17 



18 



92 



100 



104 



19 109 



20 



Sub-station No. 5. 

By transfer switches in sub- 
station No. 5, telephone 70 can be 
connected to 71-72 or 73-74-75-76- 
77-78 or to all of them in parallel. 



Sub-station No. 6. 

By transfer switches in sub- 
station No. 6, telephone 79 can be 
connected to 80-81 or 82-83-84-85- 
86-87 or to all of them in parallel. 



Torpedo F. C. S., star, for'd. 

By transfer switch in sub-sta- 
tion No. 5. telephone 88 can be con- 
nected with telephones 71-72-77. 

Torpedo F. C. S., port for'd. 

By transfer switch in sub-sta- 
tion No. 6, telephone 92 can be con- 
nected with telephones 80-81-86. 

Torpedo F. C. S., star. aft. 

By transfer switch in sub-sta- 
tion No. 5, telephone 96 can be 
connected with telephones 73-74- 

75-76-78. 

Torpedo F. C. S., port aft. 

By transfer switch in sub-sta- 
tion No. 6, telephone 100 can be 
connected with telephones 82-83- 
84-85-87. 

For'd F. C. S. 

This circuit leads direct from 
main switch panel. 



After torpedo-firing station. 

This circuit leads direct from 
main switchboard. 



Captain's battle station. 
Central station No. 1. 

By a transfer switch in central 
station No. 1, either telephone 114 
or 115 can be connected to 116-117- 
118. 

Telephone 114 is portable, and 
can be plugged in a receptacle in 
the battle station or on the bridge. 



Star, broadside 


gun No. 1 

" No. 3 

" No. 5 

" No. 7 

" No. 9 

" No. 11 
Div. Off. for'd. 
" aft. 


Port broadside 


gun No. 2 
" No. 4 
" No. 6 
" No. 8 
" No. 10 
•" No. 12 

Div. Off. for'd 
li aft. 


;' » 



Star, secondary gun No. 1 
" No. 3 
" No. 5 



Port secondary gun No. 2 
" No. 4 
" No. 6 



Star, secondary gun No. 7 
" No. 9 
" No. 11 



Port secondary gun No. 8 
" No. 10 
" No. 12 



After F. C. S. 

Torpedo firing station star, for'd. 
" " " port " 

aft. 

Torpedo firing station star, for'd. 

port 
For'd torpedo-room. 
After 

Star, engine-room. 
Port engine-room 
Steering engine-room. 



Electrical Interior Communication 



817 



Fire-Control Telephone-Circuit Switchboard. — In the preceding 

table the telephone instruments at the different stations are shown 
as grouped on twenty circuits. These circuits lead to the numbered 
circuit switches shown on the switchboard in Fig. 376, This 
switchboard is • located near the sub-stations which are grouped 




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Fig. 376. — Fire-Control Telephone-Circuit Switchboard. 

together as far as possible on a lower deck and near central station 
No. 1. This switchboard is furnished with current from a motor 
generator, shown on the left or from a storage battery SB, shown 
on the right. The leads L x and L 2 are taken from a switch on the 
interior-communication switchboard located in central station 



818 Naval Electricians' Text Book 

No. 1. To use current from the motor generator, switches A and 
and B are closed, which energizes the bus bars BB to which are 
connected all the circuit switches. The storage battery can be used 
by closing switches B and C. The circuits lead to panels in the 
different sub-stations and the current for the instruments at the 
different stations is finally distributed from these points. The 
head set shown at the bottom illustrates how the instruments are 
taken off in parallel at the different stations. 

Each circuit is provided with an impedance coil, shown at II in 
the circuit shown leading from the board. The lead from the motor 
generator has inserted in it a reversible circuit breaker CB and in 
parallel with the leads from the main switch B is a condenser CO. 
By closing the switches A and C, the storage battery may be 
charged from the motor generator. 

Telephone Circuits. — The general arrangement of the various 
circuits is illustrated in Fig. 377. This shows two sub-station, SS 
No. 1 and SS No. 2, which, in this case, are in one compartment. 
In this compartment is a transfer switch panel containing the 
switches 1 and 2. This circuit shows the means of communicating 
from the 12-inch control stations to the 12-inch turret guns. 10 is 
the forward control station and 14 is the after station; the group 
of telephones 19, 20, 21, 22 and 23 are in the forward turret and 
25, 26, 27, 28 and 29 are in the after turret. The circuits 2, 3, 4 
and 5 at the bottom lead to the corresponding numbered switches 
on the fire-control switchboard. 

When No. 2 circuit switch is closed on the switchboard, it will be 
seen that No. 10 is in communication with 11, 12 and 13. There 
is an operator at each one of these telephones with the head re- 
ceivers in place. The range, deflection and any battle orders are 
communicated over the same line, and operator at 11 takes the 
range, 12 the deflection and 13 the general orders. These orders 
are communicated to the operator at 18 who makes the connec- 
tions and passes the word given to him. If No. 10 gives instruc- 
tions to the forward turret, the operator closes switch 2 up, which 
puts his phone in connection with all the phones in the forward 
turret. When he passes the word the sight-setters at 19, 20 and 21 
get it and set the sights accordingly. 



Electrical Interior Communication 



819 



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S.S. 
NO. 2 



S.S. 
NO. 1 



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15 16 17 



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Fig. 377. — Telephone Circuits to 12" Turrets. 



820 Naval Electricians' Text Book 

If the after turret guns are to be controlled from the forward 
station, switch 1 is closed up, when 18 can pass the word to both 
turrets at the same time or only one, depending on which of the 
switches 1 and 2 are closed. 

If the forward turret is to be controlled from the after station, 
15, 16 and 17 get the word, and it is passed by an operator at 24 
who closes switch 2 down, when he is in communication on current 
from circuit 5. To communicate with the after turret from the 
after control station, switch 1 is closed down. 

Either control station can thus communicate with either turret 
or both at the same time, or one station can communicate with one 
turret, while the other can communicate with the other. 

Stowage Boxes. — All telephones except those in the sub-stations 
when not in use are kept stowed in water-tight boxes secured per- 
manently at places conveniently near where they are to be used. 
The transmitters and receivers are connected to terminals in these 
boxes by flexible conductors so they may be adjusted in place on the 
head and the operator free to move around. For the phones for 
divisional officers, receptacles are installed at suitable places, where 
the phones may be plugged in. 

For use in all sub-stations and the captain's battle station, a 
commercial form of head set combining both the transmitter and 
receivers are used, and at control stations and gun stations, the 
standard head set specially made and previously described. 

Range and Deflection Circuits. 

In addition to the telephone circuits from the various fire-control 
and sub-stations to the different turrets and guns, there are in- 
stalled wiring circuits for actuating electrical devices which give 
visual signals for sight-bar range and deflection. In general these 
devices consist of a transmitter and an indicator, the one for trans- 
mitting the desired signals, the other for indicating them. It is 
usual to use combined range and deflection transmitters, but sepa- 
rate indicators for the range and deflection. 

A general scheme of installation is as follows: In one of the 
sub-stations connected by telephone circuit to the forward 12-inch 
turret is a combined range and deflection transmitter connected to 



Electrical Interior Communication 

THOUSAND 



821 




Fig. 378. — Wiring-Diagram of Range and Deflection Circuits. 



822 Naval Electricians' Text Book 

indicators in the turret, with one range and one deflection indi- 
cator for each gun. A similar equipment gives signals to the after 
12-inch turret from the sub-station, with which it has telephone 
connection. In the sub-station from which the 8-inch turrets are 
controlled by telephone circuits is a combined range and deflection 
transmitter with range indicators and deflection indicators in each 
8-inch turret for each gun. In the sub-station controlling the star- 
board broadside guns is a separate range transmitter with range 
indicators at each gun and a separate deflection transmitter with 
deflection indicators at each gun. In another sub-station and at 
the guns of the port broadside battery there are similar devices. 

A wiring diagram showing the connection of the transmitters 
and indicators is shown in Fig. 378. 

The upper figure represents a combined range and deflection 
transmitter and consists of five horizontal bus bars, connected 
through fuses to two vertical bars. The numbered switches are 
single pole and connect the wires leading to the indicators to the 
source of current. Each switch completes the circuit through a 
glow lamp in an indicator, which, when lit, illuminates a dial 
painted with a number corresponding to that of the switch. Cur- 
rent is taken from a separate panel board which in turn receives 
current from the interior-communication switchboard in central 
station ~No. 1. The switches on the right indicate those on the 
range and deflection switch panel. The left one controls the cur- 
rent to the range bus bars and to the center bus bar which connects 
through switches to lamps on the range indicator showing " Com- 
mence " and " Cease," Co and Ce. The right-hand switch controls 
the current to the deflection bus bars. 

It will be noticed that the common negative wire simply passes 
through the transmitter but there is a wire for each separate switch. 
These wires are made up in cables and lead to the indicators where 
they are connected to their appropriate lamps. Only the wires for 
the commence and cease lamps and one from each bus bar are 
shown, so the connections are easily traced. As many indicators 
as may be desired can be wired in parallel, and in the circuit for 
the 8-inch turrets, there would be eight range indicators and eight 
deflection indicators all wired in parallel from the same wires from 



Electrical Interior Communication 823 

the transmitter, and closing one switch on the transmitter lights a 
lamp in each of the eight indicators. 

The method of signaling is apparent. If the operator in the sub- 
station gets word from the fire-control station that the range is 
8650 } T ards, it is only necessary to close switches 8 in the thousand 
(upper) row, 6 in the hundred (lower) row and 50 in the upper 
row of the range bus bars when a corresponding display will be 
made in each range indicator by the lamps 8 in the thousand row, 
6 in the hundred row and 50 in the thousand row being lighted. 
Similarly any correction for deflection is shown by closing appro- 
priate switches in the lower two bus bars. 

The separate range and deflection transmitters are entirely simi- 
lar to the combined one, but each has only two bus bars and two 
rows of switches. The bus bars are energized by the leads from 
the switch panel from one side of the switch, the common negative 
simply passing through the instrument to the indicators. 

Salvo-Firing Circuits. 

The salvo-firing circuit is wired for the purpose of giving signals 
at the broadside guns, so that all may be fired simultaneously. 
Xear each gun is installed a vibrating bell which is operated to in- 
dicate a " stand-by " signal, and secured to the person of the gun- 
pointer is a buzzer which, when the operating circuit is closed, gives 
the signal to fire. 

A wiring circuit is shown in Fig. 379. There are two panels in- 
stalled in sub-stations of the fire-control system, from each of which 
are run wires to both of the main fire-control stations. The posi- 
tive mains to which the bells and buzzers are connected in parallel 
run from the hinge side of a double-pole, double-throw switch, and 
the negative main runs direct from the main switch on the panel. 
Throwing these double-throw switches one way or another connects 
either the forward or after fire-control stations to the bell and buz- 
zer leads. By this means, the bell or buzzer signal can be given 
from either fire-control station to either the starboard or port bat- 
tery or both, but not from both stations at the same time. In the 
figure, when the double-throw switches are thrown to the right, the 
circuits to both broadside batteries are connected to the forward 



824 



Naval Electricians' Text Book 



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Electrical Interior Communication 825 

control station, and when to the left, to the after control station. 
One battery may be controlled from the forward station, and the 
other from the after station by properly throwing the switches on 
the panels. 

By an arrangement of the numbered push buttons on the panels 
either battery may be controlled from each panel at all times. As 
shown, the upper row of push buttons controls the bells and the 
lower row the buzzers. Buttons marked 1, 3, 5 and 7 control the 
starboard battery and 2, 4, 6 and 8 the port battery. 

The panel main switches are connected in parallel with the leads 
from a double-pole, double-throw switch, which can be connected to 
either the leads from a battery L X L 2 or from a dynamotor L\L' 2 . 

As actually installed, the buttons 2 and 4 control the starboard 
battery and 1 and 3 the port, so that everything connected with the 
starboard guns is on the right-hand side and with the port guns on 
the left-hand side. 

The wires leading to the fire-control stations terminate in. a 
stowage box, from which flexible conductors are lead to pear- 
shaped push buttons with two pushes. The push for the bells is 
on the end and that for the buzzers is on the side of the pear push. 
Each push is marked with the name of the battery it controls. 
When not in use the pear pushes are hung in the water-tight 
stowage box. 

Ammunition-Hoist Signals. 

Ammunition-hoist signals are installed as a means of communi- 
cation between the broadside guns and the lower decks or passages 
from which the ammunition is supplied. In general there is in- 
stalled one complete outfit of signals for each ammunition hoist. 
Each outfit consists of two indicators and a switch box, one indi- 
cator and the switch box being at the top of the hoist, the other 
indicator at the bottom. 

The indicators are entirely alike and each consists of a composi- 
tion water-tight box in which are mounted five incandescent 
5-candle-power lamps. These lamps are surrounded by cylindrical 
casings so arranged that the light from each is only given out in one 
direction, towards the cover of the containing box, which has circu- 



826 



Naval Electricians' Text Book 



lar openings cut in it covered by translucent discs. On these discs 
are painted the general battle orders, Hoist, Lower, Stop, Com. 
Shell, A. P. Shell. 

The switch box is a standard 8-way distribution box, with a 
modified cover and with interior fittings for five standard 5-ampere 








<8> 



KD 



(sH 



Fig. 380. — Wiring Diagram. Ammunition-Hoist Signals. 



switches whose switch handles are mounted on the outside of the 
cover. Each one of these switches control two lamps, one in each 
indicator, and the disc covers of these lamps have the same marking. 
The wiring plan is shown in Fig. 380. The leads L ± L 2 are run 
in conduit from the ship's lighting mains into a standard 25- 



Electrical Interior Communication 827 

ampere switch S, from which the conduit is run to the switch box. 
To operate, it is only necessary to turn the switch at the top of the 
hoist which results in lighting the two lamps, one at the top of the 
hoist and one at the bottom. These lamps illuminate the discs 
marked with the order it is desired to communicate to the ammuni- 
tion passers below. Each switch is marked with a name plate with 
the same legend as that on the lamps that it controls. 

Cease-Firing Circuits. 

Cease-firing gongs are installed for the purpose of giving a gen- 
eral signal for " cease firing." It is usual to so wire them that 
they can be controlled but from two places, the captain's battle 
station and in the main central station, which in modern ships is 
fitted as a battle station. 

The gongs are 6-inch vibrating gongs and with the electromag- 
nets wound for the yoltage of the ship's mains. They are mounted 
in each of the principal fire-control stations, forward and aft, on the 
flying and upper bridges, on the upper deck for the secondary bat- 
tery, along the main deck for the broadside battery, in all 8-inch 
turrets and in 12-inch turrets. 

The general wiring plan is shown in Eig. 381. The mains L ± 
and L 2 are taken from a switch on the interior-communication 
switchboard and lead to a transfer switch on one of the telephone 
switch panels, from which wires are run to a connection box and 
then to a feeder junction box in the captain's battle station. The 
switch TS may be used to direct the current to either the contact 
maker, switch S, in the captain's battle station, or to the switch S' 
in the central station No. 1. Erom the connection box the wires 
are run in conduit to the different points of installation of the bells, 
the circuit resembling an ordinary simple parallel lighting circuit, 
in which all branches to gongs are taken from fused junction boxes. 
All the gongs are wired in parallel and all are sounded together by 
the operation of closing the switch S, if TS is closed up, or switch 
8', if TS is closed down. 

Circuit Switch Panels. 

All telephone circuits are taken from the switchboard located in 
a place convenient to the sub-stations. The ordinary system re- 



828 



Naval Electricians' Text Book 



quires about twenty circuits which lead from the main switchboard 
to circuit panels in the different sub-stations where they are con- 
trolled by switches manipulated by the different operators. 



o 



o 



o 



-=o 



R- 



Aril 



Fig. 381. — Wiring Diagram of Cease-Firing Gongs. 



The generation and distribution of current for the talking cir- 
cuits of the telephones up to the point of leaving the switch panel 
is shown in Fig. 376. There are no calling circuits and the system 
is complete only when each telephone has its own operator. 



Electrical Interior Communication 829 

Wiring Appliances. 

The wires for all electrical means of interior communication are 
run in conduit or molding and the same appliances are used with 
these to insure thorough water-tightness through bulkheads or 
decks as are described under wiring appliances for power or light- 
ing circuits. These include different forms of stuffing tubes, junc- 
tion boxes and the like. In addition there are a few appliances 
used only on this system. They include besides those already 
described cut-out switches, connection boxes and the different forms 
of push buttons. 

Cut-Out Switches. — These are used to cut out of circuit such 
circuits that are used in ordinary times and which are wired with 
circuits that should be used in times of action. The idea is to cut 
out such exposed circuits not needed in action to prevent injury to 
them from interfering with the needed action circuits. 

A cut-out switch consists of a metal box fitted with water-tight 
stuffing glands through which the cables or wires enter the box. 
The interior of the box is fitted with a number of flat spring con- 
tacts to which the wires are connected, the springs overlapping one 
another in the center of the box on one side of a switch shaft, 
This shaft is faced on two sides with hard rubber, and when the 
shaft is turned so that one of the hard-rubber sides forces the 
spring contacts together, circuit is made through the box. 

The boxes are made in three sizes, for 8 wires, 15 wires and 20 
wires. The boxes are fitted with bosses taped for conduit, according 
to the most desirable lead for the wires. It is sometimes desirable 
to lead the wires through the bottom of the box, in which case a 
box tube is used with gland on the outside of box. The latest form 
requires the cover for the box to be of sheet brass with nipple and 
cap the same as used for feeder and junction boxes. 

The handle for operating switch in this type projects through the 
cover and acts as a " stop " to limit the throw of the switch, by 
striking against the inner side of the nipple. When the handle is 
up against the top part of the nipple, the switch is off and when 
down against the lower part of the nipple, the switch is on. 

Another type of a cut-out switch consists of a metal box with 



830 Naval Electricians' Text Book 

bosses which may be tapped to receive the conduit in which the 
wires are run. The top of the box is provided with two hinged 
doors which ordinarily are screwed down on rubber gaskets to make 
it water-tight. To open the doors it is necessary to take out the 
screws when the doors may be opened on their hinges. 

In the interior is a long row of terminal contacts to which the 
incoming wires are soldered, and each contact is secured to the clip 
side of the single-blade switch. There is a switch blade for each 
wire, and the circuit is continued through the switch to the hinge 
side where terminal pieces are soldered to the outgoing wires. All 
the switches in each box may be operated at once by one handle, 
though on account of the great number it is usual to divide the 
switches among two handles. 

The switch handles are of such size and shape that they may be 
closed or opened and the doors then shut. 

Connection Boxes. — These are used to break the leads of wires 
to take off branches and to obviate the necessity of soldering or 
making joints. They consist of water-tight metal boxes fitted with 
covers set up by wing nuts against rubber washers or with a cap 
secured by countersunk screws. When used with conduit it is 
tapped into the box and made water-tight by a gland and stuffing 
tube in the pipe near the box. When cables from molding lead 
into a box, standard stuffing tubes are used to make it water-tight. 

In the connection box, each wire of the cable has a flat copper 
terminal soldered on, on which is stamped the serial number and 
letter of the circuit to which it belongs. The terminals are then 
connected together on a metal lug secured to a porcelain base, the 
terminals set up by screws. In one form of box, the porcelain base 
is not used, the wires being spliced together and insulated. 

Push Buttons. — These are of two classes, water-tight and non- 
water-tight. The water-tight type is enclosed in a cast-brass case, 
made water-tight against a soft-rubber washer. The contact springs 
are platinum-tipped and are mounted on an insulating plate. The 
non- water-tight type is similar except it is not made water-tight, 
and is fitted with a push of hard black rubber. 

Pear buttons are fitted in quarters and offices with flexible cord. 
They are all non-water-tight. They are single, double or treble 



Electrical Interior Communication 831 

pushes made of black hard rubber, pear-shaped. The pushes are 
of metal heavily nickeled, contacts made by circular pieces of nickel- 
plated metal held away from the contact screws by small spiral 
springs. All contact points are platinum-tipped. 

Interior-Communication Switchboard. 

It is usual to install all the batteries for the interior communica- 
tion in one place, usually the dynamo-room or central station. 
The batteries for voice-tube calls, telephone calls and those for 
operating fire alarms and alarm gongs are grouped on trays in a 
locker, the trays containing not more than 12 cells each, each cell 
in a separate compartment in the tray and the trays separated by 
partitions. Each tray is fitted with handles and with bolts for 
securing in place and with a name plate indicating the circuit which 
is supplied by the battery in the tray. 

The battery terminals are connected to a switchboard from which 
the battery wires lead out to their various circuits. Telegraph 
and indicator circuits as well as those for battle-order and range- 
order circuits are connected with the generator and the current for 
them is distributed from a common switchboard with the battery 
circuits. In this way arrangement is made by which the battery 
circuits can be fed from the generators in case the batteries run 
down. This requires the introduction of a resistance to cut down 
the generator potential to that needed on the battery circuits. 

Rotary Transformer. — If a resistance in circuit is not used, a 
transformer is employed. This is of the rotary type, usually fitted 
with one armature with two windings and two commutators, one 
winding receiving the generator voltage, the armature revolving as 
a motor, which, owing to its second winding, delivers current 
through the second commutator at a reduced voltage which can be 
used on the battery circuits. (See under Dynamotor, Chapter XX.) 



CHAPTER XXXY. 

CARE OF ELECTRIC PLANT AND ACCESSORIES. 

The first requisite in the care of all electric machinery is clean- 
liness, and this refers not only to the generators and engines under 
one's care, but to all parts of the electric installation. The general 
appearance of a dynamo room and its appurtenances will be an 
index to the care given to the machines themselves. It is usually 
found that the engines of generating sets are a source of more 
trouble than the generators, mechanical faults being more per- 
sistent and more apt to occur than electrical ones, and a good 
dynamo tender should be above all a good engineer, at least as 
far as his particular engine goes. Instructions are now furnished 
with generating sets showing details of the moving parts and how 
to assemble and disassemble them, and it remains with those in 
charge to see that these are faithfully and carefully followed. 

After Stopping. 

After a machine is shut down after its usual run, it should at 
once be gotten ready for starting again, and all parts thoroughly 
cleaned and inspected. If not of the self -oiling type, all oil feeders 
should be turned off, the reservoirs filled and the cups themselves 
cleaned and the glasses polished. All oil about the engine, 
especially in the crank pits and in the foundation, should be wiped 
up with waste, and the parts dried and cleaned, the oily, dirty waste 
being immediately gotten rid of and not left in corners or out-of- 
the-way places. All moving parts should be wiped off, all bearings 
examined, and all stuffing-boxes looked at, and if there has been 
evidence of leaking during the run, they should be properly set up. 
The metallic ^packing should be removed at times and examined for 
wear, as should also the shaft bearings for an examination of the 
babbitting. All grit, dust and dirt of every kind should be carefully 
wiped off, being careful to see also that there are no stray pieces 



Care of Electric Plant and Accessories 833 

of waste left sticking to any part, -whether moving or stationary. It 
is better for this purpose to use cotton rags in preference to waste. 

If the engine is stopped with a throttle, the engine stop valve 
should be closed and also the exhaust valve, the drain valves opened 
to allow water to drain clear. 

After the generator is stopped, the brushes should be lifted and 
examined to see that they have worn evenly and have been properly 
resting on the commutator with the requisite pressure. Every part 
of the armature should be examined and turned over by hand so 
that all parts can be seen to see that there have been no abrasions 
of the windings or evidence of the armature striking the pole 
pieces. It is well to rest a thermometer on the armature imme- 
diately after stopping, covering the bulb with waste, and obtain 
the temperature before it has time to cool. The armature should 
be cleaned of all copper dust or carbon dust that may have been 
deposited from the brushes, removing it with a stiff brush or by 
hand bellows, making sure that it is dusted off and not driven into 
the windings of the armature out of sight. 

The main switch on the generator or the circuit breaker should 
be opened and all resistance taken out of the shunt-field regulator. 
The self-oiling bearing on the generator end should be examined 
occasionally, the rings cleaned, old oil replaced by clean oil. 

The commutator should be examined for any signs of undue 
wearing, cutting or burning and any evidence of the formation of 
high or flat bars, and the insulation examined to see if there are 
signs of its rising. 

If there have been any signs of weakening of insulation, the 
whole machine should be tested after every run, so that the weaken- 
ing may be properly followed and corrected before it is too late. 
This can readily be done in a few minutes by a voltmeter connected 
to the mains of another running machine, or from live bus bars on 
the switchboard. By connecting the two terminal leads of the volt- 
meter to the various parts and windings, and noting the fall of 
potential, the insulation resistance of all the parts can quickly be 
measured. The calculation is from the formula 



834 Naval Electricians' Text Book 

where V is the potential across the mains of the running machine, 
V the reading when connected between a live wire and any one of 
the various parts or windings of the machine, and R the resistance 
of the voltmeter. 

After stopping, the governor should be examined to see that none 
of the parts stick, and the parts wiped off with clean rags to prevent 
the formation of gummy substances that would interfere with their 
free working. 

All connections should be looked at, and loose ones tightened, and 
especially the connections of the different field windings, which are 
apt to be loosened by excessive vibration. Circuit breakers should 
be examined and their working parts tested. 

- After the machine has cooled and been turned over by hand to 
see that no tools or cleaning gear have been left to jam running 
parts, a cover, if furnished, should be thrown over the set to keep 
out dust or dirt. 

Starting the Set. 

Assuming that all the precautions stated above have been taken, 
a generating set should be ready to be started at an instant's notice, 
.the only time required being that necessary to warm up the engines. 

Make sure that the cylinder drains are open, and if a compound 
engine that the drain from the receiver is open. Open wide the 
exhaust valve and the engine stop valve. Turn the engine over by 
hand once or twice to make certain that nothing has been left to 
injure the moving parts. If not fitted with forced lubrication see 
that the oil feeders are opened and that the drip is properly regu- 
lated. The expansion of valves is usually more rapid than the 
cylinders, and the cylinders should reach the proper temperature 
before the full steam pressure is allowed to enter. Crack the 
throttle valve slightly and allow steam to enter the valve chest and 
cylinder, and turn over once or twice by hand to allow the steam to 
take its full course and warm all parts. In the compound engines 
there is a small pipe from the throttle to the receiver which should 
be opened to help warm. the engine. 

As the parts warm up, if there is no particular hurry to get cur- 
rent on the machine, the throttle valve can be gradually opened and 



Care of Electric Plant and Accessories 835 

the engine speeded up, noticing any leaks in stuffing-boxes or glands. 
After the engine has run at full speed for a few minutes, the 
brushes may be lowered on the commutator, if fitted that way (in 
most machines the brushes rest on the commutator all the time), 
being careful to fit the side or lower brushes first, leaving the upper 
ones to be lowered last. As soon as both brushes or sets make con- 
tact, it is probable that E. M. F. will be induced, and the handiest 
brushes to get at should be set last. The field due to the shunt 
windings will then build up and the voltage, shown on the volt- 
meter and by the glowing of the pilot lamp, will attain its full value, 
the resistance of the regulator being increased as the current rises. 
The main switch or circuit breaker can be then closed and current 
delivered to the switchboard, all circuit switches being left open. 
The outside circuits can then be thrown in one at a time, the 
brushes being examined for undue sparking and rocked accordingly 
to reduce it, and any change in the voltage being rectified by the 
shunt resistance. 

After the engine has been running for some time and it is appar- 
ent that the cylinders are free of water, the drain valves may be 
closed. If any water hammering occurs after the engine is started, 
it can generally be stopped in the compound engine by admitting 
live steam to the receiver and low-pressure cylinder. 

During the running, care should be taken to see that the oil 
feeders are working properly; feeling all the bearings with the 
hand from time to time for undue heating. If self-lubrication is 
used, the oil gauge should be connected to see that the feeding is 
under the proper pressure, from 5 to 20 pounds. After all the 
switches are closed on the switchboard, there will not be much 
change of load unless motor circuits are connected up, when the 
brushes may require some attention due to the extra load, and the 
ammeter should be watched to see that the machine is not over- 
loaded. 

Stopping the Set. 

If the load carried by a running generator which is to be stopped 
is necessary for lighting or power purposes, it should be transferred 
to another machine that has already been started and built up ; the 



836 Naval Electricians' Text Book 

circuits being thrown over one at a time on the switchboard. If the 
load is not necessary, the generator can be stopped without throwing 
off any of the circuits and this plan should be followed where pos- 
sible. The speed is slowed by gradually closing the throttle, and as 
the speed falls, the induction and current drops, gradually lessening 
the load on the machine and all lamps and wiring accessories. 
After the throttle is closed, then close the engine stop valve, open 
the drains and when the engine is entirely stopped, close the exhaust 
valve. As the voltage drops, throw out the resistance of the shunt 
field, and when current is sufficiently off, open the main switch or 
circuit breaker. If the brushes are fitted to raise, lift them clear 
of the commutator; if not, of course they require no attention. 
Then proceed as in the case given jut before starting. 

Care of the Commutator. 

As the commutator of a continuous-current machine is the most 
vital part, the utmost care should be given to its condition when 
not running, and it should be watched constantly when running, 
for under certain circumstances a few bad minutes may be sufficient 
to ruin it. Brushes must be so set that the pressure is not sufficient 
to gouge or score the commutator bars, while making such good 
contact that injurious sparking will not result. 

The commutator should not be oiled, and if any lubricating is 
necessary it can be wiped with a clean oily rag or a piece of cotton 
on which a small quantity of vaseline has been smeared ; never use 
waste, as particles are apt to be torn away and stick to the commu- 
tator. If oil is used on the commutator it is apt to char under the 
brushes, forming a film between the commutator bars, and flying 
particles of copper or carbon from the brushes may stick to it, and 
if very bad might short circuit an armature coil. Never put oil 
where it is not necessary and make sure if handling oil that none 
gets on the commutator or near the armature coils, for it may rot 
the insulation, besides making a lodging place for flying dust of all 
kinds. One good way to lubricate the commutator is to make a 
strip of canvas about the width of the commutator and put a little 
vaseline on one side, smearing it with the finger all the way across. 
Then when the machine is running and the brushes raised, press 



Care of Electric Plaxt axd Accessories 837 

the canvas with the vaseline side against the commutator. This 
is a very good way also of cleaning the commutator of any gummy 
composition that may lodge on it, using a plain strip of canvas, but 
for this purpose it should be rather coarse. 

When running, the great thing to be borne in mind is that there 
shall be no sparking on the commutator. This fault has been re- 
duced to a minimum in recent machines, the brushes requiring no 
change from no load to full load, but it should be kept constantly in 
mind and watched for, and signs of sparking in recent machines 
may mean something more than injury to the commutator. 

The commutator of modern well-designed generators should 
acquire, with proper care, a beautiful dark-bronze polished surface, 
and this is not to be taken as an indication of dirt that should be 
removed ; and a clean bright highly-polished commutator may mean 
one that has too much care. Too much care may mean too much 
use of the file or sandpaper, which should be avoided whenever 
possible. 

If the commutator has been allowed to get rough or burnt at the 
leaving edges, it may be necessary to smooth it down with a fine file, 
but this should only be done by an expert, for in inexperienced 
hands it becomes worse than which it is intended to correct. Care 
must be taken to see that an equal amount is taken off all over to 
avoid any tendency to eccentricity. Fine sandpaper fitted on a 
block of wood to the curve can be used as a finishing touch to work 
down any rough places left by the file. Xever use emery of any 
description, as the flying particles are good conductors and may 
lodge between commutator bars and bridge them over. 

If a commutator becomes so badly worn or scarred as to make 
sparking still more injurious and the heat formed a source of loss, 
it is better to place the armature in a lathe and turn the commu- 
tator down true with a tool. This should be done while the arma- 
ture is rapidly revolving and with a fine-pointed sharp diamond- 
faced tool. Only a fine cut should be taken each time and the feed 
of the tool should be very slow, and only enough metal taken off to 
insure perfect symmetry. After the tool is used, the final finishing 
may be done with a dead smooth file, and all particles of copper 
carefullv removed from between the bars. 



838 Naval Electricians' Text Book 

Care and Setting of Brushes. 

The proper position of brushes depends upon the particular wind- 
ing, internal connections, cross connections, etc., and it should never 
be assumed that the proper position is known, but the directions 
furnished by the makers should be followed. 

In many of the four-pole generators used in the service the 
armature is cross-connected, necessitating but one set of brushes 
set 90 degrees apart, the neutral position being between the poles. 
In a late design of six-pole machines there are three sets of brushes, 
the armature not being cross-connected, set 120 degrees apart and 
under the poles, the three positive and three negative brushes each 
being connected in multiple. In this machine, there is a reference 
mark on the pedestal and one on the brush-holder yoke, and when 
they are in line, the brushes are in the right position. If the 
brushes are in the exactly opposite position from what they should 
be, the machine will not build up at all, so a little experimenting 
will serve to show the correct position. The brushes should be set 
in a generator a little forward of this position, and in a motor a 
little backwards from it; this shifting being necessitated by the 
armature reactions which distort the field magnetism to a certain 
extent. 

Of whatever material brushes are made they should rest evenly 
on the commutator with sure but light pressure, about 1-J pounds, 
and anything above that merely serves to increase the friction ; the 
resistance per unit of area beyond that being not reduced. If 
brushes are made of copper, they are usually fitted so as to make an 
angle with the normal to the commutator, the angle depending on 
the construction of the brush holder and the position of minimum 
induction. This necessitates the ends being filed at the proper 
angle, and this is sometimes accomplished by placing them in a jig, 
a metal box mitered at one end to the angle desired, and the brush 
is filed down to this angle. After being filed down these are put in 
the brush holders in place, and they soon smooth down by being 
run on the commutator, the latter being harder and wearing away 
the rough edges of the brushes. 

Carbon brushes are usually set normal to the commutator, and 
are fitted for a pressure of about 1-J- pounds as stated above. They 



Care of Electric Plant axd Accessories 839 

are fitted to the curve of the commutator by passing beneath them 
fine sandpaper, held sand up against the surface of the commu- 
tator. Or the sandpaper may be pasted on the commutator and the 
brushes pressed against it while the armature is revolved, or the 
sandpaper may be passed between the brush and the commutator 
and drawn in the direction of rotation of the armature, the brush 
then raised, the paper replaced under the brush, which is then 
lowered again on it, and the operation repeated until a perfect fit is 
obtained. Carbon brushes require less attention than copper ; they 
do not cut the commutator and their resistance prevents the develop- 
ment of sparking, but this resistance causes them to heat more than 
copper, and they must be larger to carry a given current than the 
copper. At times one of abnormally high resistance may cause 
sparking, due to the fact of not making good contact with the 
commutator. 

Brushes should be set to cover as much as possible of the com- 
mutator surface, the positive and negative ones breaking joint with 
one another, and they should be shifted at times slightly along the 
commutator in the direction of the length of the bars. 

Care of Brush Rigging. — The brush rigging consists of the brush 
holders, supports for same and cables. 

The brush-holder supports are of two kinds: adjustable, i. e., 
allowing rotation of the brushes on the commutator, and fixed, 
allowing no such adjustment. The former type is used where 
exact adjustment under operating conditions is necessary and which 
cannot be predetermined in design. It consists of a ring or yoke 
carrying all brush studs, turning on a seat concentric with the shaft. 
The exact position of this yoke is determined at the time of instal- 
lation and the punch marks upon it and the stationary part of the 
machine indicating the proper position, which should always be 
kept in line regardless of the load. 

The effect of moving the brush yoke of the motors from the posi- 
tion thus designated is to alter their speed and cause sparking. 

Another type of rigging has the brush studs rigidly held by 
insulating supports from the frame of the motor, allowing no angu- 
lar adjustment of the brushes, but provided with means for moving 
the brushes toward the commutator as the latter wears. 



840 Naval Electricians' Text Book 

The studs supporting all brushes on the turning yoke are insu- 
lated therefrom by bushings and collars and are held in place by 
nuts. Care must be taken that these nuts never loosen, allowing 
the studs to turn and thus lift the brushes from the commutator. 
These nuts may possibly work loose after having been properly set 
up, and frequent inspection must be made to prevent such from 
occurring. 

Nothing is gained by increasing the pressure per square inch on 
a carbon brush above two pounds, as the resistance per square inch 
beyond this point is practically not reduced, whereas the friction 
is increased in direct proportion to the pressure. 

The tension may be determined by a small spring balance carry- 
ing a flat hook which should be slipped between the center of the 
brush and the commutator. The brush should then be pulled 
directly away from the commutator, care being taken that it does 
not bind in box, until it just leaves the same, the. tension on the 
brush being given by the reading of the balance. 

Always use the pressure of the spring upon the brush, instead of 
Jhat of the hand, when fitting with sandpaper, because if the hand 
is used the brush may be forced to take a different position from 
that derived from the spring pressure and consequently not to be 
fitted to the commutator as it should be for proper contact when 
machine is running. 

If the brush requires considerable sandpapering, No. 2 sandpaper 
may be used at first, but the final fitting must be done with No. 0. 
If an- attempt be made to fit the brushes without raising them when 
drawing the sandpaper back, it will in every case fail to give satis- 
factory results. When thick brushes are used, in addition to fol- 
lowing the above instructions the machine should be run as long as 
convenient without load in order to improve their surface. 

Care of Engine. 

In this, as in all other parts of the electric installation, the first 
requisite is cleanliness. All parts of the bright work should be 
kept bright and polished, free from oil and grease except where 
needed, and the paint work clean and free from soot and grease 
spots. 



Care of Electric Plaxt axd Accessories 811 

It is well to establish a routine for the overhauling of the engine 
parts, and not assume that because everything is working well, it 
is going to do so forever without care and time spent on it. The 
bearings and journals should be regularly examined, the caps re- 
moved and examination made for any gritty substances that may 
have been carried in by the oil. The feeding holes, or if self- 
lubricating, the feeding pipes, should be unscrewed from time to 
time and thoroughly cleaned out, as they are apt to clog after con- 
stant use. Special attention should be given to the babbitting of 
the bearings, making sure that it is wearing and bearing evenly, 
and that it is renewed in plenty of time. 

The piston-rod and valve-rod packings should be constantly 
watched and on steam leaks developing they should be taken out, 
cleaned or renewed ; the modern form all being of metallic type. 
The cylinder heads should be taken off about once a month, and the 
inside of the cylinders and pistons examined. The cylinders should 
be given a light coating of a mixture of vaseline and plumbago for 
lubrication, oil not being used in the steam spaces except under 
special circumstances. 

It is well not to touch the governor as long as it is performing 
well, for this is a most important piece of mechanism, and over- 
hauling is more likely to do harm than good. ^Yhen it fails, the 
remedy should be sought and applied, particular attention being 
given to the tension of the spring. 

The drain and relief valves should be occasionally unscrewed, the 
springs cleaned and the valves properly seated and it may be neces- 
sary at intervals to regrind them. 

Particular attention should be given to any noise or knocks that 
may develop during running. Every noise must have its cause and 
it should be at once remedied, by setting up on cross-head bearings 
or taking up lost motion or tautening on eccentrics, and experience 
alone can determine the particular kind of noise caused by any 
given fault. 

In simple engines, the valves should be so set that each cylinder 
is doing an equal amount of work, and in compound engines that 
the two cylinders are each doing their proportionate share. This 
can only be ascertained by taking indicator cards which should fre- 



842 Naval Electricians' Text Book 

quently be done and the horsepower of each cylinder calculated. 
Besides the power developed the cards will also show whether the 
valves are set for the proper lead and lap, and the general com- 
pounding of the engines. Cards should be taken at different loads 
on the generator and the voltage and current noted at the same time, 
in order that the net efficiency of the set as one may be determined. 
Each engine is supplied with a full set of tools, wrenches, span- 
ners and the like and each has its particular use, and they should 
be used for that purpose and for no other, and never allowed to be 
taken away from the dynamo-room. 

General Care of Dynamo-Room. 

The old rule, " A place for everything and everything in its 
place," is particularly applicable to ship's dynamo-rooms. Tools 
should not be left on work benches or lying around the room, but 
each should be kept in its particular place, a tool board being fur- 
nished, and all metal tools should be kept bright. Small articles 
should have a place in a locker drawer and on no account should 
they be left around or near the generators where they are liable to 
fall in the moving parts, out of sight, to be heard of later when 
they have done some damage. 

Clean waste should be kept in its own tank, and all oily waste 
should be kept in a separate receptacle, which should be emptied at 
least once a day. Oil cans and feeders should be always polished 
and kept free from oil' on the outside. Copper oil tanks, if fitted 
in the room, should be kept bright. The switchboard should be 
kept immaculately clean and copper conductors kept polished. 
Moisture should be removed at once whenever it appears on any part 
of the switchboard appurtenances, and the glass faces of instru- 
ments should be kept polished. The paint work of the dynamo- 
room should be regularly cleaned and scrubbed as well as the paint 
work on the lagging of all pipes and valves, as well as the engine 
paint work. All parts of engine bright work should have a dry 
high polish and be kept free from oil or moisture. 

The care bestowed on the floor of the dynamo-room depends on 
its character, but it must always be remembered there is more or 
less oil and grease tracked around, and the floor should be scrubbed 



Care of Electric Plant axd Accessories 843 

at times with lye water. If fitted with wire matting, that should 
be taken on deck, swept with a hard brush and scrubbed. If wooden 
gratings cover an iron deck, it is well to have them covered with 
deck cloths, well shellaced, to be used for ordinary wear, taking 
them up for inspection. 

A great deal of the oil and dirt of former days is done away with 
by the use of self-lubricating mechanism, and with care and a little 
attention, the dynamo-room should be made one of the cleanest 
parts of the ship. 

Care of Wiring Accessories. 

The greatest single cause of the breakdown of wiring appliances 
is undoubtedly water or moisture, and this should be removed at 
once, wherever and whenever it appears. The great aim has been 
to make all appliances, or at least all of those subject to exposure, 
water-tight, but the greatest care must be exercised to see that they 
remain so, and all evidence of moisture on appliances whether sup- 
posedly water-tight or not should not be allowed to remain. 

General Effect of Moisture. — Moisture on electrical conductors 
lowers the insulation resistance and if allowed to remain will event- 
ually rot the insulation and destroy it. Moisture mixed with dust 
or dirt forms a film of conducting material which is objectionable 
on all appliances, and the same may be said of oil and dirt of all 
kinds. 

Moisture may come from water thrown directly on appliances, 
such as those exposed to rain or to sea water thrown over the side, 
or from condensation from the air due to changes of humidity. 
Excessive condensation sometimes occurs in the dynamo-rooms 
when the engines are started after everything has become cold. 

All moisture tends to electrical leakage and the effect is to offer 
a path of low resistance which may injure the conductor. A high- 
resistance leak may cause trouble by the heat produced or cause 
corrosion of the wires by the electrolytic action of current of the 
water. 

Salt water is more to be avoided than fresh, partlv because it is 
a better conductor and because it deposits salt on surfaces which 
will tend to corrode by electrolysis, and in addition, the salt left 



844 Naval Electricians' Text Book 

behind will attract moisture from the air. Salt-water moisture 
should be wiped off twice, once to remove the water and the second 
time to remove the salt. Any recurring source of moisture should 
be noted and watched, the source found and corrected. Moisture 
on generators, motors, switchboards and the like should be care- 
fully wiped dry and tested for any excessive leak to ground. Moist- 
ure may often be removed from bared conductors by passing a 
current through them, starting with a small current and gradually 
increasing it, the heat evaporating the moisture. 

If by any chance armatures of motors or generators become damp 
they should be run for some time without load, allowing the heat 
to gradually dry them. 

Care and Management of Circuit Breakers. 
Type M. Q. — This circuit breaker is very simple in construction 
and requires but little attention, and there are but few matters to 
be specially borne in mind in operating and caring for it. 

1. All bearings should be well lubricated and work freely. 

2. The contact fingers must always bear evenly upon the seg- 
ment or heating will result. When inspected, it is well to slightly 
lubricate these contacts with vaseline, but care must be taken that 
too much is not used. 

3. The burning contacts above the fingers must never be allowed 
to be destroyed, as the arc will then be formed upon the fingers 
and ruin them. 

Type M. L. — The parts to be specially looked after in this circuit 
breaker are : 

1. The main brush contacts, which must be kept clean and bear 
evenly on the contact studs. 

2. The position of the armature when the circuit breaker trips. 
There should be ■£% of an inch space between the bottom of arma- 
ture and top of fiber piece on coil when the breaker trips. 

3. The secondary contacts must be kept in good condition and 
care should be taken to see that they make good connection until the 
main brushes have well cleared the stud. In adjusting the second- 
ary contacts, see that there is between J and -f^ of an inch space 
between the moving plug contact and the fixed contacts on the side 



Care of Electric Plant and Accessories 845 

of the fiber chute when the circuit breaker is open. This adjust- 
ment is made by removing the top pole piece and fiber cover of the 
chute, when the secondary contact is exposed. Also, in renewing 
the secondary contacts, see that all set-screws and connections are 
firmly set up, as a loose contact in this circuit breaker may destroy 
the main brush. 

If the main brushes should become burned so that it is necessary 
to dress them with a file, see that they are so filed and adjusted 
to the stud that the outer tip of the brush just comes in contact 
witli the stud when the heel of the brush is ■£% of an inch away. 
This insures that every lamination of the brush comes in firm con- 
tact with the stud when the circuit breaker is closed. 

Keep the armature pivot and brush holder well lubricated, also 
all joints connected with the tripping catch. It is well when exam- 
ining the secondary contacts to slightly smear with vaseline. This 
prevents the cutting action and increases the life. 

Care of Fuses. 

To Install or Replace a Fuse. — Open the switch controlling the 
circuit the fuse protects. 

Stand on insulating material; do not touch grounded metal and 
if possible use insulated tools. A slight shock might cause the 
dropping of a tool that might short circuit other parts of the circuit. 

Do not allow the screws holding a fuse to fall, as they are liable 
to lodge in some place where they might short circuit a live circuit. 

In replacing fuses, set up on one end lightly, keeping the other 
end pointed away from its contact, then swing the free end to its 
contact and set up on both screws. 

Branch fuses can be replaced without opening the switch on the 
circuit, the glass being held firmly in the middle and pressed 
squarely into the contact clips. It is well to light up the interior 
of the box by an outside light so there will be no danger of touching 
the wrong clips and melting the fuses. 

In working near switchboards with screw-drivers it is well to 
wrap all the blade except the tip with tape to prevent accidental 
short-circuiting and one working with the body close to switchboards 
and especially near bus bars should not wear watch chain which 
might rub against the bars and cause momentary short circuits. 



846 Naval Electricians' Text Book 

Care and Management of Rheostats. 

Three points should be particularly observed in the care of 
rheostats : 

1. All electrical connection should be tight and clean. 

2. The filling should not be overheated so as to destroy the con- 
ductor or its insulation. This is something which is not likely to 
occur, as the rheostats have been designed with special reference for 
the work to be performed and should give no trouble except in ex- 
treme cases of careless operation. 

3. The rheostats should be kept dry. Moisture absorbed by the 
asbestos insulation will cause leaks and short circuits, and it is 
essential that particular care be taken that no water enter the 
rheostat. The fillings are protected by a coating of japan to protect 
them from moisture. As this japan may be injured by extreme 
heating, the rheostats should be occasionally inspected. If the 
japan is found to be injured the filling should be painted with it. 
When the panels are freshly painted, a moderate amount of heat- 
ing will cause them to smoke, but this does not indicate trouble 
unless the smoke should be excessive. The smoke from newly- 
painted rheostats will ordinarily disappear after the rheostat has 
been used a few times. 

Care and Management of Controllers. 

It is essential that the separate parts of all controllers should be 
kept bright and clean. Bearing should be occasionally lubricated 
with oil and contact rings occasionally lubricated with vaseline, but 
pains should be taken not to use too much, as it is apt to increase 
the burning and the blackening of the contacts. Care should be 
taken that the gaskets of controllers having water-tight covers 
should not become broken or loosened, but that they should always 
be in place and the cover tightly clamped. Attention should be 
given also to the bushings surrounding the lead wires, where they 
come through the frame of the controller, to make sure that they 
have not slipped out of position. The stuffing-boxes at the top, 
when such are used, should be kept well packed, so that water will 
not enter around the shaft. Controllers are generally provided 
with a projecting brass ring, called a water cap, which, while not 






Care of Electric Plaxt axd Accessories 847 

being absolutely water-tight, answers all ordinary requirements of 
the water protection. The projections on the shafts and other 
bright steel parts should be occasionally slushed to prevent rusting. 
All screws and check nuts should be kept thoroughly tight, as a 
loose electrical connection is likely to produce excessive heating. 

Adjustment of Contact Segments and Fingers. — Care should be 
taken that the contacts and fingers are kept in good condition. 
They should always present a smooth appearance, except that the 
tips of the contact rings and the fingers will be slightly burned and 
roughened through continued use. A small degree of roughness is 
expected, but it should not be allowed to be so great as to interfere 
with the easy mechanical operation of the controller, or with the 
electrical connections. The contacts should be frequently in- 
spected, and the fingers and contact rings filed, if necessary, to 
remove any rough spots, so that when on any notch of the con- 
troller, the finger where it makes contact with the line ring, will 
make contact across the whole width of it, and not in a single point. 

If the rough spots are so bad that they cannot be easily filed 
smooth, the contact ring or tip should be replaced by a new one. 
In some cases, as already explained, the segment will have to be 
replaced, while in others a short tip only is removed, leaving the 
main jDart of the contact undisturbed. When replacing the con- 
tacts, take care that the surface of the back of the contact and of 
the outside of the c} T linder castings are bright and clean. The 
screws supporting the contact rings should be set down sufficiently 
to make a firm contact, but it is very easy to set the screws too 
hard, in which case it will be difficult to remove them later, after 
replacing contacts. 

Fingers are easily replaced by taking out the small screws fasten- 
ing the spring to the finger base. This spring is bent so as to give 
about the correct tension when screwed down firmly in place, but 
the fingers should always be tried by hand to make sure that the 
tension, when pressing upon the cylinder contacts, is correct. This 
tension, for 1-inch fingers, should be about three pounds, that of 
the smaller fingers being correspondingly less. A set-screw is pro- 
vided with each finger, bearing upon the projecting lug of the 
finger base. This screw should be turned until it allows the top 



848 Naval Electricians' Text Book 

of the finger to drop about -/% i ncn below the surface of the contact 
finger of the cylinder. The check nut should then be firmly set, 
taking care not to twist the spring of the finger by so doing. If 
this distance is greater than -f% inch each, the contact fingers are 
likely to interfere with the free movement of the cylinder, as the 
ends of the fingers will strike against the ends of the segments, and 
if the amount is less than -£% inch the fingers will not drop suffi- 
ciently when the cylinder contact leaves it to bring the burning in 
the proper place. As it is essential that the surfaces making electri- 
cal contacts should be kept smooth, it is necessary that the burning 
should take place at some other point, and this is accomplished by 
this movement of the finger, causing the actual burning to take 
place near the top, beyond the line of contact of the contact finger 
at the end of the round. 

While a roughness at the extreme tips of the contact fingers and 
contact segments does not impair the electrical contact at the work- 
ing points, still it makes the controller more difficult to operate 
and makes the break between the finger and contacts uncertain and 
uneven, so that it is important to keep the surfaces as smooth as 
possible. In adjusting the fingers, the springs should be bent, if 
necessary, by a small wrench, so that the finger will bear upon the 
contact ring throughout its entire width, and not at one corner only. 

It is important that all the fingers which make or break electrical 
connections with the contact rings on the first position of the con- 
troller should do so at the same instant, or as nearly so as possible. 
It is not always possible to accomplish this absolutely, because the 
fingers may vary slightly in shape, and if the fingers are adjusted to 
make exact contact on one side of the cylinder, they will not do so 
on the other side, but this difference should be equalized as much as 
possible between the two sets. This adjustment may be made by 
turning the cylinder toward the first position until the contact 
rings touch the cylinders, and after a little practice it will be easy. 
Note whether any of the contact fingers are lifted by the contact 
ring before the rest, and all such should be raised slightly with 
the adjusting screws until all of the fingers are observed to rise and 
fall together, but in making this adjustment the dropping distance 
of -fe of an inch should not be much increased or decreased. If 



Care of Electric Plant and Accessories 849 

this becomes necessary, it shows that the contact point of the finger 
is not at exactly the right distance from the spring. This can be 
remedied by taking off the finger and either straightening it with a 
hammer or bending it slightly more. If it is found, after making 
an adjustment of the fingers on one side, that they do not make con- 
tact together on the other side, those that touched too late should 
be let down, and those that touched too soon should be raised up 
until about the same amount of difference occurs on both sides of 
the controller ; but a finger which touches too soon on one side will 
touch too late on the other. 

When the contact fingers are properly adjusted as above, a nearly 
equal sparking should occur at all of these contacts when the 
cylinder is turned off, and this forms an additional test of proper 
adjustment. If one finger should draw considerably more arc than 
the rest, it shows that it breaks contact a little before the rest. It 
is not expected that the sparking at all points can be made exactly 
the same, or if so, that it will always remain so, but it should be 
approximately equal. In this way the burning of all fingers is 
reduced to a minimum. 

Operation. — In using the controllers, special care should be ob- 
served to make the changes of position quickly, as the burning of 
the contacts is very much reduced. This should be observed, both 
in making and breaking the circuit, but especially in breaking it. 
If two electrical contacts carrying a current are pulled apart slowly 
an arc will be formed which may be continued for some time, but 
if they are pulled apart very quickly to the proper distance, the arc 
will last but an instant. The position of the cylinder being indi- 
cated by the star-wheel, it is very easy to tell how far the cylinder 
has moved. 

Care should always be taken that the cylinder should stop only 
in points corresponding to notches on the star-wheel, as otherwise 
the controller might be held up with the contacts separated so little 
that the arc would continue. In turning the controller from the 
off position the pressure of the cylinder contacts against the ends of 
the fingers will be felt before the first notch of the star-wheel is 
reached. This offers about the same amount of resistance as the 
star-wheel notches, and unless care is taken it may be confused 



850 • Naval Electricians' Text Book 

with, one of these notches. Particular pains should therefore be 
taken that in turning to the first position the cylinder actually 
reaches this position and does not stop when the first blow of the 
contacts is felt. 

Although the controller should be turned quickly from one notch 
to the next, it does not follow that a controller should be turned 
rapidly from the off position to the full-speed position. To do so 
would cause an overload, which, might open the circuit breaker. 
It is therefore advisable that several seconds be taken in bringing 
the motor up to full speed, the actual length of time depending 
upon the size of the motor. In the case of the larger motors, five 
seconds should be sufficient to bring the motor up to full speed; 
in the smaller motors, two or three seconds. The proper way is to 
pass quickly each notch, pausing an instant on the notch before 
proceeding to the next one. In turning the controller off to stop 
the motor, in most cases the cylinder can be turned instantly to the 
off position. This can be done in all cases of series motors, but in 
the case of the shunt motors, when lowering heavy loads, or in lift- 
ing very light loads, it is better to turn off the controller more 
slowly. If a light load is stopped too suddenly, the momentum of 
the armature, if it is short-circuited on the off position, will pro- 
duce a rush of current which may tend to burn the brushes and put 
too much mechanical strain on the motor and the mechanism to 
which it is connected. This should be observed with special care 
in the case of the turret controller, as the momentum of the turret 
is so great that it should not be started or stopped suddenly. In 
lifting a heavy load with an ammunition hoist, there will be no 
great difficulty in stopping the motor from full speed instantly. 
A sudden stop is not recommended when the empty cage is being 
lifted. 

Care and Management of Turret-Turning System. 

The following description applies to motors controlled by the 
Ward-Leonard System of Control. 

Equalization of Load between Motors. — If it is found that one 
motor is taking considerably more current than the other when 
both fields are approximately the same temperature, and so far as 



Care of Electric Plaxt axd Accessories 851 

is known, no resistance has been inserted in either field, after going 
over all connections and making sure that the trouble is not due 
to a loose contact, the load should be readjusted by moving the 
brush yoke upon the motor which is taking the greater load. 

This adjustment can only be made by trial, and after moving the 
yoke a small amount in one direction, the turret should be revolved 
and the effect noted on the ammeters. This operation should be 
repeated until the current through each motor is the same. 

The current in the motors should not differ more than 15 or 20 
amperes ; but even when they run with exactly equal currents when 
the turret is revolved in one direction, a greater difference than this 
may occur when the direction of rotation is reversed. Unless the 
constant difference is more than 40 to 50 amperes no attempt 
should be made to equalize the load. 

If the two motors should tend to run at widely different speeds, 
one may drive the other as a generator. This would be imme- 
diately apparent on the ammeters, one of which would read in the 
opposite direction from which it should. 

Lubrication. — The self-oiling bearings of the motor should be 
kept full, frequent examinations being made, however, to see that 
no oil is working into the motor case. 

Order of Operating Apparatus — Using Main Generator to Start. 
— In the turret : 

1. See that the controller is in the off position, that the current 
breaker is open, and that the field and armature switches are closed. 

In the dynamo-room : 

2. See that all switches and circuit breakers on the system con- 
nected to the generator to be used, are open. These are : 

(a) Generator panel circuit breaker. 

(b) Equalizer switch. (Never close this switch when operating 
a turret.) 

(c) All switches on the generator panel. 

(d) Armature and field switches on the power panel board. 

3. Close single-pole series field switch at bottom of panel, for the 
machine to be used. 

4. Close single-pole switch to common negative on panel of ma- 
chine to be used. 



852 Naval Electricians' Text Book 

5. Close single-pole switch to positive turret bus bar on panel of 
machine to be used. 

6. Close field switches for turret to be operated on panel of 
machine to be used for operating it. 

7. Close double-pole motor-field switch on main power panel. 

8. Close single-pole switch on the main power panel in negative 
side of generator — motor-armature circuit. 

9. Close circuit breaker on top of generator panel. 
In turret: 

10. Close circuit breaker in turret. 

11. Operate controller. (See following instructions:) 
To Stop. — In turret : 

1. Throw the controller to the off position. 

2. Open circuit breaker in the turret. 
In dynamo-room: 

3. Open the circuit breaker on the generator headboard. 

4. Open armature switch on main power board. 

5. Open the field switch on the main power board. 

6. Open all switches on the generator panel. 

7. Stop engine. 

Directions for Operating the Turret Controller. — The turret 
should not be accelerated too rapidly as this requires an excessive 
current and will result in blowing the circuit breaker. Practice 
will soon give the operator a knowledge of just how quickly it may 
be brought up to speed, and then no trouble will be experienced 
with the circuit breaker, which will only act as intended in case of 
accident. The circuit breaker should never be closed until the con- 
troller is brought to the off position, as a sudden load would be put 
on the system causing the circuit breaker to open again. 

In starting from rest, the controller wheel should be quickly 
moved to the first notch, or until the armature circuit is closed. 
After that, the rate of movement is immaterial, as the only circuits 
opened and closed are those of the field of the generator, which 
carry a small current only, and the circuit breaker is thus the 
governing factor. 

In stopping the turret, the controller wheel may be rapidly turned 



Care of Electric Plaxt axd Accessories 853 

to the first notch, thus causing the motors to generate current and 
thus retard the motion of the turret. When the speed of the turret 
has been materially reduced, the controller may be thrown to the 
off position, in which the brake circuit becomes operative and the 
motors stopped. By this method the arcs at the controller fingers 
are diminished, the wear on the friction discs is reduced and exces- 
sive strains are not brought to bear on the armatures of the motors. 

In starting the turret when very fine arcs of train are required, 
the controller wheel should be quickly revolved to the second notch 
or thereabouts and immediately returned to the off position, allow- 
ing the brake circuit to act. Under no circumstances should the 
controller wheel be thrown beyond the off position to reverse the 
motors before the turret has stopped as this will certainly open the 
circuit breaker. 

In case of failure of power, throw the controller at once to the 
off position and investigate the cause. As the circuit breaker in 
the dynamo-room may cause this, by opening, and as the operator 
may close it immediately, it is essential that the controller be at 
once thrown to the off position to prevent an excessive rush of cur- 
rent when this closing takes place. 

Cautions — Using Main Generator. — 

1. The equalizer switch must never be closed. 

2. The motor-field switch must always be closed before the arma- 
ture switch. 

3. In case one motor in the turret must be cut out, open the 
armature switch first and then the field switch in order that the 
armature may never receive current without an excited field. 

4. Xo switches on the generator panels should be closed for tur- 
ret turning except those for the turret to be used. 

5. The series-field shunting switch should always be open when 
the generator is not operating a turret. 

6. The turret must not be accelerated too rapidly, and the cir- 
cuit breaker in the turret must never be closed until the controller 
is at the " off " position. 

7. The controller should not be rapidly thrown to " off n position 
when the turret is running at full speed, except in cases of 
emergency. 



854 Naval Electricians' Text Book 

8. If the armature current fails, the controller should imme- 
diately be thrown to " off " and the cause of the trouble investi- 
gated. 

9. Never reverse the direction of the motors until they have first 
been stopped. 

Care and Management of Turret-Ammunition Hoists. 

Solenoid. — Oil holes are provided in the top of the solenoid 
casing. These should receive attention when running, and if the 
brake shows a tendency to heat, oil should be used. 

To start: 

See that the controller is on the off position and the circuit 
breaker open; then: 

1. Close switch on power panel in dynamo-room. (This excites 
the auxiliary distribution boards in the turret.) 

2. Close double-pole switch on panel. 

3. Close circuit breaker. 

4. Operate controller. (See directions below.) 
To stop: 

1. Throw controller to off position. 

2. Open circuit breaker. 

3. Open double-pole switch on panel. 

4. Open switch on main power panel in dynamo-room. 
Directions for Operating Controller. — 

1. Turn the handle to lower, as marked on the dial plate. 

2. Throw handle promptly from the off position to first notch, 
and do not let it stop when the fingers first touch the contacts or 
an arc will be started and the fingers roughened ; also be careful not 
to move past a notch and then return to it or an arc will be drawn. 

3. When starting the hoist do not accelerate the car too rapidly, 
but make a short pause on each controller notch. If too rapid a 
start is made the current will jump to very large values and open 
the circuit breaker and roughen the fingers. 

4. When stopping the car at the bottom after lowering, do not 
try to stop suddenly from full speed, as the rush of current when 
the armature is short-circuited at the off position will be excessive. 



Care of Electric Plant axd Accessories 855 

5. When stopping the car at the top after hoisting, throw the 
handle quickly to the off position, as at this position the solenoid 
brake sets and holds the load. 

6. If the circuit breaker acts, throw the handle immediately to 
the off position. 

Care and Management of Chain-Ammunition Hoists. 
Hoist and Gearing — Lubrication. — 

1. The sprocket wheels, chain links and gears should be slushed 
with a mixture of graphite and grease. 

2. All shaft bearings should be oiled by hand as use requires. 

3. The hand gear sprockets and chains should be oiled and turned 
over at intervals to prevent rusting. 

4. The upper sprocket wheels, which turn on fixed pins, are pro- 
vided with oil holes. 

Adjustment. — 

1. Any stretch or slack in the sprocket chain can be taken up by 
screwing down on the adjusting screws of the bearings of the 
sprocket shaft. 

Solenoid Brake. — The brake should be so adjusted, by means of 
the turnbuckle at the end of the brake band and the nuts on the 
vertical rod supporting the movable case, that when the magnet is 
released the cores do not fall more than 1J inches, and when the 
magnet is energized the brake band does not rub on the wheel. 

The leather lining on the brake band should be kept clean and in 
good condition, and the bearing pins in the lever should be occa- 
sionally oiled. 

Location of Safety Devices. — The location of safety devices which 
may open the circuit are as follows: 

1. Fuses and switch in dynamo-room. 

2. Fuses in box in each feeder circuit. 

3. Fuses on face of controller panel. 

4. Overload circuit breaker. 

5. ^"o-load circuit breaker. 

6. Switches on controlling panel. 



856 Naval Electricians' Text Book 

To start : 

1. Close switch on panel in dynamo-room. 

2. Close interlocking switches on controlling panel in the proper 
direction, throwing them up to hoist and down to lower. 

3. Move the rheostat arm as far as possible to the right, setting 
the circuit breaker. 

4. Press down on push button and move the arm slowly to the 
left until the button rests in the raised surface of the contact ring. 

If the arm is moved too rapidly, or if the current fails, the cir- 
cuit breaker will open. 
To stop: 

1. Open the single-pole, single-throw switch, or pull out the push 
button in starting arm. 

This will release the circuit breaker which is in the side of the 
line. It is impossible to re-set this until all starting resistance has 
been placed in the circuit. The single-pole switch should always 
be left open, except when the hoist is in operation. 

2. Open the switch in dynamo-room. 
Caution. — 

1. Before starting the hoist, always see that the hoist cover is 
removed and the delivery table turned out of the hoist and pinned 
in position, and the wrench for operating the safety pawls removed. 

2. Before lowering, always see that the safety pawls are raised. 
Failure to follow these two precautions will jam the hoist and may 
result in damage to the mechanism. 

3. Before hoisting ammunition, always see that the safety pawls 
are down. 

4. Always see that hand gear is thrown out and power gear 
thrown in before starting the motors to operate the hoist. 

Care of Boat-Crane Gear. 
Lubrication. — 

1. The motor-armature bearings should be kept well full of 
grease and all gears should be slushed as use requires. 

2. The solenoid brake should be well oiled through the hole pro- 
vided to prevent excessive heating. 



Care of Electric Plaxt axd Accessories 857 

3. The worm for hoisting and revolving gears runs in oil, and 
these oil boxes should be kept well filled. These boxes also supply 
oil to the worm bearings. 

4. All other bearings to hoisting and revolving gear are fitted 
with oil holes. 

5. Hoisting blocks and guide sheaves are fitted with oil holes. 

6. Main deck bearings are fitted with oil holes for roller bearing. 

7. The steel hoisting cable should be kept well coated with a 
mixture of grease and graphite. 

Care and Management of all Ventilation Sets. 

Brushes. — In view of the continuous character of the work re- 
quired of the ventilating sets, special attention must be paid to the 
brushes to keep them in good condition. 

Lubrication. — All motor bearings are fitted with self -oiling rings, 
oil-pockets, gauge-glasses and stop-cock. The oil-pockets should be 
kept full to the marks on the gauge-glass. If filled too full, the oil 
will work over into the machine, which would quickly destroy the 
insulation. 

Location of Safety Devices. — The following safety devices may 
open the motor lines : 

1. Switch and fuse on switchboard in dynamo-room. 

2. Fuses on controlling panel. 

3. No-load and overload device on controlling panel. 
Order of Operating Apparatus. — To start : 

1. When a fan is fitted to run at different speeds, turn the field 
resistance arm at " slow." 

2. See the switch on panel board open. 

3. Close switch on power panel in d} T namo-room on required 
blower lead. 

4. Close switch on controlling panel. 

5. Move starting arm from initial position slowly across the 
armature starting-resistance contacts, until no-load coil holds it in 
the extreme position. 

6. If a variable speed motor, the speed may then be increased 
by slowly moving the resistance arm from slow towards fast. When 



858 Naval Electricians' Text Book 

necessary to reduce the speed, this arm should he moved very 
slowly to allow the fan time to slow down, as otherwise the motor 
may act as a generator, due to its momentum, and generate a back 
current sufficient to blow the fuses. 
To stop: 

1. Open the switch on the controlling panel. The starting arm 
will take care of itself. 

2. Open switch on power panel in dynamo-room. 

Bearings and Lubricants — Description and Care of Bearings. 

The bearings in electric machines are of four kinds: 
Self -oiling. 
Sight feed. 

Compression grease cups. 
Grease. 

Self-Oiling Bearing. — This consists of a removable sleeve resting 
in a support above a pocket in which is placed the oil supply. It 
is cut transversely across its upper half by one or more slots, in 
which are placed rings carrying the oil to the bearing surfaces. 

These rings are of larger inside diameter than the shaft and rest 
upon it, the bottom of them dipping into the oil in the reservoir 
below. As the shaft revolves it turns the rings, thus continually 
bringing oil from the supply and delivering it to the top of the shaft 
where it is passed along the bearing out at the ends of the sleeve 
and back to the reservoir. 

Thus the supply is constantly in circulation, all dirt settles to 
the bottom and clean oil is fed to the bearings. 

The oil well is filled through holes in the upper part of the bear- 
ings and emptied through oil cocks at the bottom. 

The quantity of oil in the reservoir is indicated in a gauge which 
has a mark upon it showing the height to which the bearing should 
be filled. The bearing must not be filled above this mark, or the 
oil will run out of the ends and collect in the machine, causing 
trouble in the windings. 

There is a vent in the top of the gauge which must be kept open 
or the confined air in the glass tube will prevent the oil from cor- 
rectly indicating the height to which it has reached in the bearing. 



Care of Electric Plant and Accessories 859 

Care must be taken that the oil rings are always in position. 
They should be frequently examined to see that they are revolving 
and feeding properly. This may be easily done by touching the 
ring with the finger, and observing if oil is left upon it, being par- 
ticular not to introduce dust into the bearing in this way. 

The ring must never be allowed to stand still upon the revolving 
shaft, as a depression will soon be worn on its inner surface, which 
will prevent it from ever again operating properly. 

The covers or plugs for the holes through which the box is filled 
must always be kept in place to prevent dirt from entering the 
bearings. 

Eed Engine Oil is recommended for use with these bearings, and 
those kinds which will thicken, such as sperm oil, must not be used, 
as they are liable to obstruct the rings and prevent them from 
turning. 

Sight-Feed Bearings. — These bearings consist of a sleeve resting 
in the pillow block with a hole on top midway of its length into 
which the oil is fed from a reservoir above. The oil passes along 
the shaft to the ends of the sleeve where it is caught and collected 
in a receptacle. 

The oil is conducted through a brass pipe to the bearing, and 
from it to the receiving tank below. The rate at which it is fed is 
graduated by the valve in the sight gauge near the supply. 

The control of feed is accomplished by turning the milled head 
on the gauge. 

These bearings should be frequently examined for undue heat. 
Special care should be exercised in this matter with relation to the 
bearing between the armature and the fan because it supports the 
latter and is subject to much harder usage than the one at the 
commutator end ; also, it is less accessible and therefore more liable 
to be neglected. 

Compression Grease Cups. — Bearings on certain machines are 
oiled by means of ordinary compression grease cups. The grease 
should not be forced from these cups under too great pressure, as it 
is liable to collect upon and be thrown from moving parts after 
passing through the bearings. 



8G0 Naval Electricians' Text Book 

Grease Bearings. — These bearings consist of split sleeves held in 
supports, with reservoirs above and below. The upper half of the 
lining has a horizontal slot allowing the grease in the box to feed 
to shaft. 

The box above should be kept full of grease, which should be 
pressed down before starting the motor, in order to be certain that 
it is in contact with the shaft. If this is not done, and the grease 
has hardened or contracted since the previous run, the bearings must 
reach a sufficiently high temperature to melt the grease above before 
it will be lubricated. This delay might cause injury to the linings. 

Bearings of this type are frequently mounted upon motors for 
boat crane, rammers, elevators and whip hoists. 

Care of Bearings. — Attention must be given to all bearings while 
running. 

Under proper conditions no reasonable excuse can be offered or 
accepted for abnormal heating. If it exists, it needs immediate 
investigation and remedy. 

After being in operation a short time, a certain amount of heat 
is imparted to the bearings by the armature; any undue heating 
aside from this requires an immediate remedy by the attendant. 

The temperature may reach blood heat when running with full 
load. 

Undue heat may result from a variety of causes. Among these 
may be mentioned insufficient quantity or poor quality of lubricant ; 
dirt or gritty matter in oil or bearing; a badly-scraped bearing; 
rough journal; caps too tight; an armature shaft slightly bent, or 
bearings out of line. 

If from any cause a bearing becomes unduly warm, a liberal sup- 
ply of oil may be sufficient to check the heat. If it gets very hot, 
cold fresh oil will benefit it. It is not advisable to use water on the 
interior of the bearings unless sure that it is free from dust and 
gritty particles, although in case of emergency water or ice upon the 
outside of the box of ironclad motors may be used to reduce the 
temperature of the bearings. 

If the box has a split lining, the cap should be slightly loosened. 

If a hot box develops, the shaft should not be stopped imme- 
diately, but slowly reduced in speed until the temperature has 



Care of Electric Plaxt axd Accessories 861 

fallen to a safe limit. If this direction is not followed, the sleeve 
is liable to contract upon the shaft so tightly that it cannot be re- 
moved except by cutting it off. The shaft is also likely to be 
injured by such an action. 

The cause of the heating should always be ascertained and reme- 
died, and the boxes removed, cleaned, scraped and accurately refitted 
before starting up again. 

After removing the pillow block, or lining, be scrupulously care- 
ful in replacing to see that the contact surfaces and dowel pins are 
free from grit, fibers of waste, or any kind of dirt. 

If the bearings should become considerably worn, there is danger 
that the armature may rub upon the pole pieces. By observing the 
position of the armature in the field, it may readily be seen whether 
the bearings are worn down to any considerable extent. If they are 
badly worn vertically, or horizontally, new sleeves or linings should 
be substituted. 

Lubricants. 

The speed at which the machine runs requires a lubricant 
especially adapted to it. 

The value of a lubricant depends upon its power to reduce fric- 
tion and prevent the excessive development of heat. The character- 
istics which should be possessed in order to be most efficient as a 
lubricant are : 

1. Sufficient density or body to keep the surfaces between which 
it is interposed from coming in contact under greatest pressure. 

2. The greatest adhesion to metallic surfaces and the least cohe- 
sion in its own particles. 

3. The fluidity of the oil should be as much as is consistent with 
the above conditions. 

Keep the oil and grease free from gritty matter. All foreign 
substances injure the quality of lubricants and tend to increase the 
heating of bearings. 

Xew oil should always be filtered. 

The oil in self-oiling bearings should be kept at the proper height 
by additions, but after a bearing is once in good condition it should 
not require complete renewal for several months, although judgment 
is necessary to determine just when a change should be made. 



862 Naval Electricians' Text Book 

When the oil is renewed, the oil-well should be carefully cleaned 
and all thick oil and sediment removed. 

It is impossible to recommend any one grade or kind of lubricant 
for continual use because the value of the lubricant depends upon 
the temperature of the atmosphere where it is used ; consequently, a 
grease which would be satisfactory on bearings below the protective 
deck, where the temperature might be fairly uniform, would perhaps 
be entirely unsatisfactory in bearings exposed to the weather, where 
wide variations of temperature would be expected. 

The exact grade of lubricant is, therefore, dependent upon the 
judgment of those responsible for the plant, it being necessary to 
use a much harder grease in warm climates than in cold. 

Inspections. 

The following are given as general directions: 

Motors. — Lubrication must be in proper condition. 

Brushes must be frequently examined, and see that the screws 
for holders have not become loose. 

Motors should be examined to see that moisture or oil does not 
collect inside in the bottom of the frame. This is especially appli- 
cable to the boat crane and turret-turning motors. If found, it 
should be removed immediately, and not allowed to drip on the 
armature or commutator. Drain-cocks are provided in turret-turn- 
ing, boat-crane and whip-hoist motors. 

The motors should be run as often as convenient for a sufficient 
length of time to allow them to become warm in order to drive off 
moisture. 

Controllers. — The interior of all controllers must be inspected 
after each time used and all burns or roughness on either fingers 
or contacts made smooth with a file and fingers properly set as 
previously described. If this is neglected the fingers may catch on 
the cylinder making it difficult to move the same, even if in the 
attempt the finger is not crippled. Too much emphasis cannot be 
given to this, as neglect might cause a controller to give trouble at 
a critical moment. 

All boat-crane controllers must be kept tight in every way, as 
water accumulating in them will certainly give trouble. 



Care of Electric Plant axd Accessories 863 

Rheostats. — Eheostats should be kept dry and as free from dust 
and dirt as possible. Every rheostat is insulated from the frame of 
the ship by special bushings to reduce the possibility of trouble at 
this point. The exposed surfaces should be kept clean to prevent 
leakage over them and thus make then valueless, and if broken must 
be renewed. 

If a rheostat gets wet it should be carefully wiped and dried 
before being put to regular use. If convenient it may be dried in a 
warm room, but if not, then by care it may be gradually warmed by 
allowing a current to pass through it until all moisture has been 
expelled. This may be done after it has been ascertained that 
dampness is the cause to be removed, by placing the rheostat in a 
circuit which will not allow more than one-fourth of the usual cur- 
rent carried by the rheostat to pass, and as the temperature rises 
and no trouble develops, gradually increasing the current until the 
normal amount flows. It may be left in this way until all moisture 
has been expelled. All dust should be removed as far as possible, 
and for this purpose a bellows or blast of dry air is very convenient. 

Circuit Breakers. — All circuit breakers should be examined at 
least once a month to see that the bearing contacts are in proper 
condition, and that all other parts are in good condition. 

Covers for circuit breakers in boat cranes and whip hoist must 
be kept water-tight and should be examined frequently to see that 
such is the case. 

Important Instructions for Operation. 

There are certain general operations which should invariably be 
done in the same manner when managing electrical apparatus and 
which have been given in the preceding under the heads of different 
appliances described. These are collected and given below in two 
lists, " Always " and " Xever," in order that they may more easily 
be remembered and referred to. 

" Always." 

Always close the field switch before the armature switch. 
Always open the armature switch before the field switch. 



864 Naval Electricians' Text Book 






Always open switches carrying field currents slowly, allowing the 
field discharge to dissipate at the contacts. 

Always close switches provided with field-discharge resistances as 
far in as they will go. 

Always open the series-field shunting switch on the main switch- 
board after operating a turret. 

Always throw a controller to the " off " position immediately 
when the circuit breaker opens. 

Always see that the arm of the automatic release rheostat on 
controlling panels comes to the " off " position when the main 
switch is opened. 

" Never." 

Never close a series-field shunting switch on the main switch- 
board unless the generator is to operate a turret. 

Never run a controller between notches. 

Never trip the automatic overload on a ventilating motor-con- 
trolling panel to shut down the motor. 

Never open the field circuit of a motor while the main switch is 
closed. 

Never hold the car of a 12-inch ammunition hoist on any con- 
troller notch but the " off " position. 

Never run a 12-inch gun-elevating motor at full speed when near 
the end of its train, or when depressing an empty gun or elevating 
a loaded gun. 

Never start an ammunition-hoist motor until the hoist cover has 
been removed and the delivery table turned out into position. 

Never start an ammunition-hoist motor in the lowering direction 
until the safety pawls have been raised. 

Care of Switches. 

Blisters and burns should be removed from all switches as soon 
as they appear, as they make poor contact when the switch is again 
used and increase the resistance. 

The joints of knife switches should be sufficiently tight to hold 



Cake of Electric Plant and Accessories 865 

the blade in any position in which it is placed, but not so tight they 
cannot be conveniently opened or closed. 

Circuit switches should be thrown quickly in either direction to 
prevent arcs being formed which injure the contacts. When opened 
the switch should be fully open and the blades not left near the 
clips. 

Turret-field switches should be opened slowly to allow the in- 
duced current of the motor field to discharge through the field- 
discharge resistance (a special resistance being fitted for this 
purpose) . 

Before opening the field switches of generators, the self-exciting 
switches, throw the field rheostat to "Low" and open when volt- 
meter stops moving towards zero. 

In double-throw switches fiber blocks are f urn* shed to slip in the 
clips of the switch not being used. These should always be placed 
in position. 

Care and Management of Search-Lights. 

To Place Lamp in Projector. — See that the clutch securing the 
barrel in position as to elevation is caught and then take off the 
front door. Do not leave this against anything but place it imme- 
diately in its own box for safe keeping. The magnet piece sup- 
porting the two shutters of the obturator is turned up to allow the 
lamp to pass under. Place the back end of the lamp on the slide 
and holding the front end up push the lamp in until it falls into 
the slot in the slides and then lower the front end. Push the lamp 
in until the focusing screw is engaged, and then the lamp can be 
moved with the wrench supplied for that purpose. Do not lift the 
lamp by the carbon carriers but by the body of the lamp. After 
the lamp is placed turn down the magnet piece. 

To Place the Carbons. — Separate the carbon carriers by means of 
the socket wrench as far as possible. First, place the negative 
carbon, the one towards the mirror, with the end even with the 
carbon clamp and set up on the contact screw. Next place the 
positive carbon with the point about J inch from the negative 
carbon and the end projecting through the clamp ; then set up on 
the contact screw. Bring the points opposite each other by means 



866 Naval Electricians' Text Book 

of the vertical and horizontal tangent adjusting screws. Before 
turning on the current, the points should be brought within J inch 
of one another and the feeding screws should be turned to see that 
they work freely. 

Operating. — The one in charge during operation should never 
leave the projector, but should constantly watch the burning of the 
carbons and the focusing of the lamp. If the crater is not burning 
in the center, the positive carbon must be changed by the vertical 
and horizontal screws and the arc drawn to the center. This is 
done by a wooden-handled socket tool through the side sliding door. 

If from any cause the lamp feeds until the carbons touch they 
must be drawn apart by hand, using the crank-handle wrench pro- 
vided for the purpose. 

If mushrooms form on the negative carbon they must be broken 
as soon as possible (when the neck gets small), and this can be 
done by moving the positive carbon quickly up and down, striking 
the mushroom and breaking it off. 

Do not keep the beam of light higher than 40 degrees above the 
horizontal for any length of time, as pieces of incandescent carbon 
may fall on the mirror and break it. 

Focusing. — This is done by the focusing screw by which the lamp 
is moved nearer to or further away from the mirror. The most 
satisfactory focus is found when the beam of light is thrown with 
minimum divergency. If the beam is diverging the lamp must be 
moved away from the mirror, if converging it must be moved nearer 
the mirror. 

Extinguishing. — Before turning off main switch, see that all pro- 
jector doors are closed. This is to prevent cold air from getting 
inside the projector as it might crack the hot mirror. After the 
lamp is extinguished and cooled, it should be cleaned free from dirt 
and carbon dust. Brush the dust from the lamp with the brush 
furnished and do not blow it off, and see that it does not fall into 
the mechanism. Dust mirror with dry rag and polish with chamois 
skin. Do not expose mirror to direct rays of the sun. 

The only parts of the lamp requiring oil are the feeding screws 
and pivots of feeding armature, for which clock oil should be used, 
and this very sparingly. 



Care of Electric Plant axd Accessories 867 

Care of Night-Signal Set. 

Most of the troubles of the night-signaling apparatus arise in the 
cable leading from the keyboard to the lanterns, as this is exposed 
constantly to the weather and to the heat and gases from the smoke 
pipes. The keyboard is made water-tight and can be installed under 
cover and it ordinarily gives no trouble, if kept clean and is handled 
with care. The plug on the cable end which carries the contact 
points for the leading wires can only be inserted in one position as 
the receptacle has a pin which engages a slot in the plug. There is 
a nut on the end of the plug which should be screwed tightly against 
the soft-rubber packing after the plug is inserted. It is a good 
plan when the plug is well home and there is no necessity for its 
removal to serve the whole plug with small stuff and cover it with 
painted canvas to help keep out water from the contact points. 

Another detail requiring attention is the soft-rubber packing used 
about the couplings and the rubber gaskets at the lanterns through 
which the cable leads. These are apt to become hard and dry, 
allowing water to get in to the lamp connections. They should be 
watched and replaced when necessary and the whole gasket and 
gland should be well taped over. 

The cable can be renewed, one conductor at a time, if any should 
have become burnt out or rotted due to moisture and heat. The 
only trouble in renewing a conductor comes in making the connec- 
tion to the plug. This is in three parts, the upper part screwing 
into the middle and the middle into the lower containing the con- 
tacts. The upper part can be unscrewed and pushed up along the 
cable without any trouble. The middle part can be unscrewed after 
coming up a set screw, and the gasket for the whole sixteen cables 
must then be worked along the conductors so the middle part can 
be drawn from the lower to get at the contacts. When this is 
accomplished the old conductor can be unsoldered and the new one 
soldered in its place and then passed through the proper hole in the 
gasket and through the other two parts, which can then be 
assembled. 

From time to time the whole cable should be treated with some 
form of tar, as ship's rigging is, for protection against rain. 



868 Naval Electricians' Text Book 

Care of Truck Lights. 

As in the case of the night-signal set, most of the trouble comes 
in the cable. Particular attention should be paid to the receptacles 
for the cables to see that they are at all times thoroughly water- 
tight. The stuffing-boxes on the lanterns should be screwed down 
hard on the gasket and the whole thing, stuffing-box, gasket and all, 
should be thoroughly taped. After a long time the contacts in the 
controller may get discolored and burnt and the cover should be 
taken off at intervals and the contacts brightened up. 

Care of Diving Lantern. 

The main care of this is, of course, to keep it water-tight. The 
cable is brought out from the lamp terminals through a metal cap 
through a water-tight gland packed with a soft-rubber gasket pass- 
ing through the handle of the lantern. On each end of the lantern 
is a metal cap, the joint between the metal cap and the glass being 
packed with a soft rubber. 

A lamp can easily be replaced by removing the side rods which 
bind the two caps together, when the whole lantern comes apart- 
easily. It is advisable to take the lantern apart frequently for the 
purpose of renewing the washers as they tend to vulcanize under 
the hard pressure. The cable gasket should also be frequently 
renewed. 

When the lamp is used under water, moisture will be deposited 
on the inside of the lantern and this can be drawn out by unscrew- 
ing a large-headed screw tapped into one of the metal heads. When 
the moisture is removed the screw should be set tight, and a rubber 
washer placed between the screw-head and the cap. 

Care of Connection Boxes. 

Most of the trouble in the cables for the various battery and 
generator circuits for interior communication occurs in the connec- 
tion boxes, through dampness. The connection to the connection 
boxes, whether from conduit or from molding, is made water-tight 
by a gland and a soft-rubber gasket. The boxes have water-tight 
covers with wing nuts and the covers should always be set up tightly. 



Care of Electric Plaxt axd Accessories 869 

Oxidation of the terminals is apt to occur, forming verdigris, which 
should be at once removed. The cover gasket and conduit gasket 
should be examined periodically and renewed if necessary. If 
moisture is found in a box it should be thoroughly dried before the 
cover is replaced. 

Care of Appliances. 

The greatest care should always be taken to see that thorough 
water-tightness is preserved throughout the whole wiring system. 
The glands of stuffing tubes through bulkheads and decks should 
be occasionally examined, and if necessary the packing renewed and 
the glands set up tight. The covers of all junction boxes and water- 
tight boxes of every description should be always screwed down 
tight on the rubber gaskets and the screw caps set up tight. The 
chains to the caps should always be intact, so there is no possibility 
of the caps becoming mislaid. Especially should this be the case 
with switches which require the removal of the cap before the switch 
can be turned. After using such a switch, the cap should at once 
be replaced. After using a receptacle, it is most necessary to 
see that the cap is replaced to avoid risks of short circuit and to 
keep out moisture. The caps of water-tight accessories should never 
be removed unless in case of necessity. Curiosity is not a sufficient 
necessity. The covers of most boxes are finished in a dull black 
and these should be occasionally wiped off with a clean rag slightly 
oiled to remove am^ traces of oxidation or verdigris. They should 
not be painted. 

Fuse boxes should be looked at occasionally to see that only 
proper fuses are used. This is frequently necessary in the fire- 
rooms, where firemen have a habit of replacing burnt fuses by nails 
or pieces of wire. 

When canvas covers are fitted, they should be kept on habitually 
when appliances are not in use or when they are not required to be 
off for inspection. Covers should be kept in proper condition and 
should be water-tight for those exposed to the weather, as for search- 
lights, telegraphs and indicators, etc. These covers should be re- 
moved and replaced by the dynamo-room force. 



870 Naval Electricians' Text Book 

Care of Fixtures. 

All fixtures are either silver-plated or bronze, and the bronze 
fixtures can be kept clean by wiping with a clean rag slightly oiled, 
but the oil should be wiped dry. Permanent fixtures usually do not 
require much attention, but movable ones are apt to show oxidation 
due to the handling they get from the moisture of the hands. It is 
not advisable to use polish on the silver-plated fixtures as most 
polishes contain acids which attack the plating. A dry powder may 
give a polish with good effect if used properly and sparingly. 

The globes of all ceiling fixtures should be removed at times and 
wiped clean and dry, both on the inside and outside. Dust is bound 
to collect in these globes. If occasion requires it, they can be 
washed with hot water and soap, but must be thoroughly dried. 
The globes of steam-tight globe fixtures should be removed at inter- 
vals and cleaned and polished with clean waste. Incandescent 
lamps should be thoroughly clean on the outside, and opal shades 
should be kept free from dust. 

Undoubtedly the greatest sources of grounds on lighting circuits 
come from the use of portable fixtures, and the greatest care must 
be taken with these, and any fault at once repaired. This is par- 
ticularly true of deck lanterns and portables used in the fire and 
engine-rooms, subject to moisture or to great heat. All portables 
should be periodically overhauled to see that the connection to the 
fixture is water-tight, and that the receptacle plug is properly 
wired and free from short circuits. The conductors used with 
portables in coal bunkers or fire-rooms frequently break down in 
their insulation, being left to rest on hot ashes, or covered with coal 
that tears off the braid. 

Care of Store-Rooms. 

Nothing indicates the general condition of an electrical plant bet- 
ter than the orderliness and cleanliness of the store-rooms for 
electrical supplies. The room should be provided with proper 
lockers, shelves and drawers, and it is a good plan to mark with 
name plates what the various compartments contain, so in case 
anything is needed in a hurry, it can be found without overhauling 
a lot of unnecessary articles. Lamps are kept in specially-prepared 



Principles of Wireless Telegraphy 871 

shelves and the different candle-powers should be grouped together. 
Wires should be kept on reels, properly marked with the number of 
feet and its size. Small wires can be kept in coils, hung up over- 
head. All small articles such as screws should be assorted in sizes 
and kept in appropriate boxes, and interior fittings should be laid 
out flat and neatly arranged. Care should be taken with these to 
see that the porcelain bases are not broken or chipped. 

Portable fixtures, such as signal lanters, battle and deck lanterns, 
have their conductors coiled up neatly around them and hung on 
hooks from overhead. It is a good plan to tag them with the color 
of the lenses and the length of conductor they are fitted with. 

Special care should be taken with breakables, such as globes, 
shades, spare lenses, spare screens, and it is a good plan to keep 
them packed in excelsior and in a separate locked compartment. 

Spare conduit or molding can usually be kept overhead along the 
beams, and elbows or bends can be kept in barrels or laid out on 
shelves. 

All instruments should be kept in their individual cases and kept 
locked if fitted to do so. 

As far as possible the floor space should be kept free to allow as 
much space as possible for moving around and handling stores. 
A certain amount of small stores will necessarily be kept in the 
dynamo-room, but only such articles that are needed in a hurry, 
and all others should be kept under lock in the store-rooms. No 
one but those authorized to do so should ever be allowed to take 
articles from the store-rooms, for in this way only can a proper 
expenditure be kept. 

Spare armatures should not be allowed to rest on the deck, but 
should rather be mounted on a shaft raised from the deck, and 
turned now and then. They should be properly wrapped to prevent 
injury and covered entirely to keep out dust and dirt. Spare parts 
of engine should be kept together, coated with tallow and white lead. 



CHAPTEE XXXVI. 
PRINCIPLES OF WIRELESS TELEGRAPHY. 



PAET I. 
DEFINITIONS. 

An alternating current is one that periodically reverses its direc- 
tion in its circuit, flowing first in one direction and then in the 
other. This alternating current is due to an alternating E. M. F., 
that gradually increases from zero to a positive maximum then de- 
creases to zero, and then reverses its sign, increases to a negative 
maximum and then decreases to zero. 

The greatest positive or negative values of the alternating cur- 
rent is called the amplitude of the alternations. 

Each complete set of operations is called a cycle. 

The time that elapses between the commencement of the current 
in one direction and its beginning again in the same direction is 
called a period. 

The number of periods per second is called the frequency of the 
alternations. 

A high frequency alternating current is one in which the fre- 
quency is reckoned in thousands, and, for convenience, if the fre- 
quency is above 1000, such an alternating current is said to be of 
high frequency and below that number it is said to be of low 
frequency. 

An electric oscillation is defined to be an alternating current 
whose frequency is reckoned in the hundreds of thousands, the 
amplitude of each alternation being less than the preceding one. 

Sustained oscillations are those in which the alternations are 
very rapid and do not lessen in their amplitude. 

Damped oscillations are those consisting of a limited number of 
alternations, the amplitude of each of which is continually de- 
creasing. 

Under damped oscillations, if the lessening of the amplitude is 



Prixciples of Wireless Telegraphy 873 

very rapid, they are called strongly damped oscillations, and if it 
is slow, they are called feebly damped oscillations. 

Capacity. 

All conductors have capacity, depending on their form and size. 

The capacity of a conductor is greatly increased when it is 
placed near a conductor electrified with the opposite kind of 
charge, so therefore a greater quantity of electricity may be put 
into it before it is charged to an equal degree of potential. 

An arrangement for holding a large quantity of electrification 
is called a condenser. 

The capacity of a condenser depends upon : 

1. The size and form of the conductors, usually metal plates or 
coatings. 

2. The distance between the conductors. 

3. The capacity of the material (dielectric) separating the 
conductors. 

The dielectric separating the conductors must be of necessity a 
non-conductor, the usual form being either glass, air, mica, or oiled 
paper. 

The effect of introducing a condenser into a circuit carrying a 
continuous current is to completely stop the current, as the di- 
electric is a non-conductor, but on introducing it into an alternating 
current, the effect is different. The alternating current simply 
passes into and out of the condenser, changing its sign, as the cur- 
rent charges it first positively and then negatively. The effect is 
to hold back the current from the E. M. F. impressed in the circuit, 
and the current is said to lead the E. M. F. 

The total charge in a condenser depends on its potential and its 
capacity, and the potential depends on the source of electricity to 
which it is connected, and by which it is charged. 

The practical unit of capacity is the farad, and is equal to 10 9 
of the absolute unit of capacity, and is the capacity of a condenser 
that will be charged to a potential of 1 volt by 1 coulomb. The 

microfarad is one-millionth of a farad, or 1?0Q i ?000 X 1?0 oojoo,000 
= 10 -15 absolute units. The capacity of all condensers is stated in 
microfarads. 



874 Naval Electricians' Text Book 

Induction. 

The phenomenon of induction has been explained in previous 
chapters, and it has been shown how currents are induced in con- 
ductors when they are moving in a magnetic field, or when there is 
any relative change in the number of lines of force cut by the 
conductor. 

If the magnetic field surrounding a conductor carrying a current 
is changed due to changes in the current itself, there is induction 
produced which reacts on the current producing the change in the 
field. This is not marked in a straight conductor but if it is coiled 
into a spiral the magnetic field due to each coil reacts on the 
others and produces greater changes in the flow of current, and the 
effect is still more marked if the coils are wound on a core of iron. 

This phenomenon of self-induction acts to oppose changes in the 
current; that is, if the current is increased, self-induction opposes 
the increase, and if decreased, it opposes the decrease. 

The total amount of cutting of lines of force by a circuit when a 
current of 1 ampere is turned on or off in it is called the inductance 
of the circuit and is denoted by the letter L, and is numerically 
equal to 

T SxN 

where 8 = number of turns in a coil, 

N = number of lines of force due to C, 
G = current in amperes. 

The practical unit of induction is called the henry and corre- 
sponds to a cutting of 10 9 lines of force when 1 ampere is turned 
on or off. 

As self-induction resists changes in the flow of current, its 
effects are strongly manifested in currents of constantly changing 
flow (alternating currents). The resistance of a conductor due 
alone to changes of current is called its reactance. 

The combined effect of the resistance (ohmic) and the reactance 
is called the impedance. 

The effect of introducing inductance in an alternating circuit is 
to cause the current to lag behind the impressed E. M. E. and thus 
capacity and inductance produce opposite effects. 



Principles of Wireless Telegraphy 875 

PAET II. 
PRODUCTION OF HIGH FREQUENCY OSCILLATIONS. 

A necessary feature of wireless telegraphy requires the produc- 
tion of high frequency electrical oscillations, and this necessity 
will be shown when the operation of conveying the electrical energy 
from one point to another is considered. 

The electrical discharges necessary to the formation of electric 
oscillations may be produced by an ordinary Ley den jar, by a 
condenser, by an induction coil, or by a combination of any of 
these. The" discharge from any of these electrical contrivances 
may be continuous, intermittent, or oscillatory. The discharge of 
a Leyden jar or a simple condenser appears to be practically in- 
stantaneous, but as a matter of fact, experiment shows that usually 
it is oscillatory, the period of oscillation being so short that the 
discharge appears as a single spark. If the discharging circuit 
could be made without resistance, it is likely a Leyden jar would 
exhibit a discharge that would oscillate backwards and forwards 
from one coating to another, the difference in potential between the 
two coatings becoming less and less, finally arriving at a common 
zero potential. 

The effect of introducing resistance is to choke down the oscil- 
latory discharge, a discharge through a high resistance giving a 
series of strongly damped oscillations which soon dies away. 

Production of Electric Oscillations by the Discharge of a Con- 
denser. — If the two conductors of a condenser are brought to dif- 
ferent potentials and they are suddenly connected through a 
conductor having inductance but small resistance, experiment shows 
that the equalization of their potentials takes place by means of a 
discharge consisting of a series of damped electrical oscillations. 

There are many mechanical analogues that may be used to show 
the similarity of damped oscillations, a common one being a simple 
pendulum. When the pendulum is hanging up and down and 
motionless there is the force of gravity acting on its bob, but no 
turning moment, as the arm is zero. As the bob is drawn from 
the vertical and held at some point, there is now a turning moment 
tending to return it to its original state of rest. This is the pro- 



876 Naval Electricians' Text Book 

duct of the force of gravity multiplied by the horizontal distance 
it has been displaced. The difference between the two forces in the 
two cases corresponds to the difference of potential in the case of 
the conductors of the condenser. When the bob is released, it 
passes through its zero position and swings to the other side, due 
to the inertia of the mass of the bob. The distance it will be 
displaced on the opposite side is less than the- distance it was on 
the first, and when again at rest, it swings back, passes through zero 
and again to the first side with decreased swing. This action goes 
on with continually decreasing swing until brought to rest. All 
the distances on one side correspond to positive potential, those on 
the other to negative, and they are gradually brought to a neutral 
or zero potential when the bob is at rest. 

The necessary conditions for the creation of mechanical oscil- 
lations are that the thing moved must tend to go back to its original 
position when the restraining force is withdrawn and must have 
sufficient inertia to overshoot the position of equilibrium in so 
doing. 

In the same way the necessary condition for establishing electri- 
cal oscillations in a circuit is that it must connect two bodies having 
capacity with respect to one another and the circuit must possess 
inductance and low resistance. 

Fundamental Equation of Wireless Telegraphy. — The electrical 
factors controlling the discharge of a condenser are the ohmic 
resistance of the circuit, the capacity and inductance in the circuit. 
If R = resistance in ohms of the circuit, 
K = capacity in farads, 
L = induction in henries, 

then if R > y-^ there will be no oscillations in the electrical 
discharge, but if 



n<n 



there will be oscillations. 

In the latter case, if the number of oscillations is n the oscilla- 
tions will be such that 

4X 2 * 



u = Vx 



Principles of Wireless Telegraphy 



877 



If R is small, 



or 



2tt\/KL ' 

the circuit vibrates in its natural period equal to 

T = 27r\/KL. 
Apparatus for the Production of Intermittent Damped Oscilla- 
tions. — The usual method employed for the production of electric 
oscillations is the discharge of a condenser of some kind, the charge 
and discharge being repeated at regular intervals. 

The connections of the apparatus are shown in Fig. 382. 




Fig. 382. — Elementary Sending Circuit. 



I shows an induction coil, whose primary terminals are connected 
to the source of supply of electric current marked L x and L 2 . One 
plate of each of the condensers K is connected to the terminals of 
the secondary coil and the other plates are connected in series by 
the inductance coil L. The terminals of the secondary coil are 
also connected by the spark gap S. 

When current is sent through the primary coil of the induction 
coil, at each interruption by the hammer H, an E. M. F. is created 
in the secondary coil. This charges the condensers, the plates con- 
nected with the secondary with opposite charges, and those con- 
nected with the inductance L of opposite charges, and also oppo- 
site to the other plates. The first result of interrupting the primary 
may be then as represented in the figure by the algebraic signs. 

When the spark balls S are a suitable distance apart, the con- 



878 Naval Electricians' Text Book 

densers being fully charged, the difference of potential between the 
plates of each breaks down the insulation of the air between the 
spark balls and the charged condensers discharge themselves 
through the spark gap, the outer plates neutralizing themselves 
through the inductance L, setting up oscillatory discharges in this 
coil and it is then said to vibrate electrically. 

Electrical Vibration of the Inductance. — It has been shown 
above that the natural vibration period of the circuit containing 
the inductance depends upon both the induction and capacity of the 
inductance coil and is numerically equal to 2-ir^KL. 

Just before the condensers discharge themselves, the total energy 
is all electric, and at the instant that discharge takes place, the 
opposite charges move towards each other in the inductance. Dur- 
ing this act of neutralization of potential, a magnetic field is set 
up around the coil, and at the instant of neutralization, all the 
electric energy has been converted into magnetic energy. The 
strength of this magnetic field depends on the amount of the 
moving charges and on the inductance of the conductor. 

If there has been but one charging of the condensers, there will 
be but one discharge, and the magnetic field set up around the 
inductance having no continuous source of supply, will collapse on 
the coil, and the magnetic energy will be converted into electric 
energy, charging again the condensers, but with a less charge than 
before, due to the energy lost in heating the wires. The phenome- 
non is then repeated, the energy being first electric, then magnetic, 
and so on until the charges are fully neutralized. 

If there is a continuous source of supply of E. M. F. and the 
condensers are being continually charged and discharged through 
the spark gap and the inductance coil the magnetic field induced 
around the inductance coil cannot collapse on the coil as other 
fresh fields are continually being set up, and as a consequence the 
magnetic field radiates off into space, producing the so-called electric 
waves. 

Senders. 

The purpose of all senders is to produce high frequency electric 
oscillations. The general method of producing these oscillations 
has been illustrated in Fig. 382, but a more general method, illus- 



Principles of Wireless Telegraphy 



879 



trating practically all the principles of wireless transmitters is 
shown in Fig. 383, known as the Tesla apparatus. 

In this elementary figure are represented all the elements of 
transmitters for the production of high frequency electric oscilla- 
tions. The elements are made up as follows: 
L X L 2 = lines for the supply of E. M. F. 
V ■=. primary of the induction coil. 
I" = secondary of the induction coil. 
CC ==■ choking coils to extinguish the arc at the spark gap. 
S =■ discharge spark gap. 
K = condenser. 
L = inductance. 

/'" z= primary of oscillation transformer (air core). 
7 IV = secondary of oscillation transfer. 
S' = discharge spark gap of oscillation transformer. 



L, 



L 2 




Pig. 383. — Complete Typical Sending Circuit. 



Arc Stoppers. — Due to the alternating current produced in the 
secondary coil of the induction coil, there is a tendency to the pro- 
duction of an arc across the spark gap which would lessen the pro- 
duction of oscillations, and the choking coils CC are introduced to 
prevent this, and with the spark balls a suitable distance apart, 
the only spark that will pass will be that due to the discharge of 
the condenser. 

Oscillation Transformer. — The primary circuit of this trans- 
former T" is placed in series with the condenser and spark gap, 
and this constitutes the circuit in which the electric oscillations are 
set up by the discharge of the condenser. These oscillations act 
inductively on the secondary coil, and if this coil has a larger num.- 



880 Naval Electricians' Text Book 






ber of turns than the primary the difference of potential at its ter- 
minals will be greater than in the primary by the ratio of the 
capacities. 

When the primary circuit V is excited, high potential high fre- 
quency oscillatory sparks will pass between the spark gap S'. 

The other elements of this circuit have been previously de- 
scribed. 

Practical Apparatus for the Production of Damped Oscillations. 

The elements necessary for the production of intermittent 
damped oscillations have been shown in Figs. 382 and 383. 

Though an induction coil is shown as the means of producing 
high electromotive force, any other type of generator of high electro- 
motive force might be used. In the majority of practical appa- 
ratus, the induction coil, the primary of which is excited by an 
interrupted continuous current, or alternating current, either direct 
or produced by some sort of transformer is used. 

The construction of an induction coil suitable for wireless use 
has been described in Chapter VIII. 

An ordinary induction coil can be employed as an alternating 
current transformer by removing its interrupter attachment and 
supplying the primary direct with the alternating current. For 
use on shipboard where alternating currents are not available it is 
usual to make use of a motor-generator, the motor end being 
wound for continuous current from the constant potential mains 
and directly connected to an alternating current armature, this 
arrangement transforming the low potential of continuous current 
into potential of alternating current. This alternating current is 
then supplied direct to the primary, and in the form of induction 
coils generally used, a potential of 20,000 to 30,000 volts can be 
obtained from the condensers. 

If the continuous current is used, the use of some form of inter- 
rupter is necessary. These are generally of one of the following 
classes: hammer, dipper, motor turbine, or jet, and electrolytic 
interrupters. 

Although all these present peculiarities, the one in general use is 
the turbine or mercury jet interrupter. In this a jet of mercury is 



Principles of Wireless Telegraphy 881 

forced out of a small aperture against a metal plate, and the jet is 
interrupted by means of a toothed wheel, rotated by a motor, which 
also works a centrifugal pump by which the mercury is squirted. 
In another form a jet of mercury is thrown on a metal plate and is 
made intermittent by revolving the plate, the current passing 
through the mercury. The mercury is covered with oil or alcohol 
to prevent oxidation. The length of the revolving plates or seg- 
ments as well as their speed can be varied and so the number of 
interruptions is well under control. 

Electrolytic interrupters present marked peculiarities, in which 
an electrolytic cell of dilute sulphuric acid as the electrolyte and 
electrodes of lead and platinum are used. Under certain condi- 
tions of E. M. F., current passed through this cell will interrupt 
the circuit periodically and an enormous number of interruptions 
can be made. 

Condensers. — A condenser in its most general form consists of a 
pair of conducting surfaces separated by a dielectric. Glass, mica, 
or micanite, and ebonite are about the only solid dielectrics suitable 
for condenser construction. 

A condenser in ordinary use is the Ley den jar, being a glass jar 
coated inside and outside with tin foil, the tin foil secured to the 
glass with a thin shellac varnish. These jars are made in various 
sizes, and as usually made will stand charging to about 20,000 
volts. They are arranged to be connected in series or parallel. 
The inside coating of each jar is connected by some positive form of 
connection to a terminal leading through the top of the jar and to 
connect in parallel, all these terminals are connected together and 
the outside coatings are connected by the jars resting on a common 
connecting plate. 

Plate Form. — Another form of condenser is constructed by cover- 
ing flat sheets of flint glass with tin foil on both sides, leaving a 
margin of glass all around with the exception of a small strip on 
each side which is allowed to project over the edge of the glass, this 
projection on each side being on opposite corners of the plate. A 
number of plates are made this way and are then built up, laying 
them back to back and front to front, so the corresponding termi- 
nal strips on each will coincide, and they are secured together, and 
all the strips of each are connected to common terminal contacts. 



882 



Naval Electricians' Text Book 



Variable Condensers. — Where variable small capacities are re- 
quired they are made with flat plates with air dielectric, the plates 
arranged so they can be moved to or from each other. 

In another form, a number of fixed pairs of quadrant-shaped 
plates of brass are placed one above the other in an ebonite box, 
and all are connected together and to one terminal on the box. In 
the center is a pivotted vertical rod carrying a number of brass 
plates which are spaced apart the same distance as the fixed plates. 
The arrangement is such that every other plate is a fixed one, and 



\ 



Slaby-Arco. 



-o o- 






' r m% 




Massie. 



De Forest-Shoemaker. 



v 

Fessender. 



Stone. 



Fig. 384. — Sending Circuits. 



O 

o 
o 
o 



o 
o 
o 
o 



w 



every other one a movable one. When the movable plates are 
turned so as to be directly under the fixed ones, they act as condenser 
plates, and when turned away they vary the capacity. The dielec- 
tric can be air or the plates can be immersed in some form of 
insulating oil. 

There are several other forms of variable condensers used, made 
on the step-by-step principle or of the sliding type. The former 
have a definite number of capacities depending on the number of 
steps, while the latter has any number of capacities between the 
maximum and minimum values. 



Principles of Wireless Telegraphy 883 

Inductances. — Variable inductances for transmitting circuits are 
almost invariably made on the sliding principle. The variable in- 
ductance usually consists of large, bare wire wound in a helix on an 
insulating frame, with the turns widely separated and fitted with 
sliders by which more or less turns can be connected to the cir- 
cuit. Other sliders are provided by which more or less turns can 
be connected between the aerial and ground. 

Sending Circuits. 

The following elementary diagrams show the sending circuits of 
the various forms of wireless sets used on ships of the Navy, and it 
will be seen that they all conform to the general principles as illus- 
trated in Fig. 384, the differences being in minor changes in the 
arrangement of the essential parts. 

In each case, the lines leading from the left are connections from 
the secondary coils of the induction coil. 

These are all direct-connected sets with the exception of the Stone, 
which is an example of inductively connected aerial. 

PAET III. 

ELECTROMAGNETIC WAVES. 

The energy of the sending instrument is conveyed to the re- 
ceiving instrument through the atmosphere, practically, or at least 
theoretically, through the all-pervading ether that permeates all 
space and bodies. The present accepted theory regarding the trans- 
mission of electricity is that it is due to a series of whirls or streams 
of bodily movements in the ether, and the energy is conveyed from 
one point to another by vibrations of the ether particles, in a man- 
ner similar to that in which light is propagated. Just as a lumi- 
nous body sets up vibrations in the ether, so do electrical oscilla- 
tions when rapid enough cause bodily motion of the substance of 
the ether, these movements taking the form of waves that travel 
through space with the same velocity as light. These undulations 
are partly electrical and partly magnetic, the vibrations causing 
each being at right angles to each other and both are at right angles 
to the direction of the propagation of the waves. The movement of 



884 



Naval Electricians' Text Book 



the ether particles is restricted to extremely small ranges of dis- 
tance, the wave form travelling on as in the case of water waves, 
where the particles of water simply vibrate np and down. 

It has been shown by experiment that these electrical waves have 
many of the properties of light waves and can be reflected, re- 
fracted, and polarized. They also have the property of passing 
unchanged through brick, stone, or woodwork and through many 
substances that are opaque to light. 

Properties of Electric Waves. 

Considering an ordinary wave as produced by simple harmonic 
motions of the particles of ether, each particle vibrating in its 
own plane at right angles to the onward direction of the wave and 
each particle differing in phase by a certain definite ratio from 
another, the onward form of the wave in a single plane would 
have the shape of the curve of sines. 





Fig. 385.— Wave Form. 



In the wave form shown in Fig. 385, the distance od is called the 
amplitude, being equal to the greatest displacement of the particles 
from their normal position along the line ac. The wave length is 
the distance ac, and at c all the particles are in the same relative 
phase as at a. 

The period is the interval of time which is taken by the particles 
in passing through all the relative phases from a to c, or at the 
end of one period, all the particles are in the same relative phase 
as at starting. The period of the wave length determines its fre- 
quency, the shorter the period, the greater the frequency and vice 
versa. The number of waves that pass a given point in a certain 
interval multiplied by the length of one wave gives the total dis- 
tance travelled by the waves in the given interval, and if that inter- 
val be unity, the distance travelled becomes the speed or velocity of 
the propagation. 



Principles of Wireless Telegraphy 885 

The amplitude of the waves depends upon the energy of the 
electrical discharge producing the waves, just as the amplitude of 
sound waves caused by a vibrating string depends upon the energy 
with which the string is plucked. The number of vibrations de- 
pends upon the electrical characteristics regulating the discharge, 
independent of the energy, in the same way that the pitch of sound, 
or the number of vibrations, produced by a vibrating string is 
dependent upon its length and independent of the energy setting it 
in vibration. 

If v = velocity of propagation, 

A = the wave of length, 
n = the number of vibrations, 
then v = n\. 

As the velocity of light waves and electrical waves, according to 
the accepted theory which has been well verified by experiment, is 
equal, it follows that the number of electrical waves multiplied by 
the length of one wave must be equal to the velocity of light. 

Experiment shows that the length of electrical waves compared 
to those of light waves is very long, so the frequency of these waves 
compared to light waves must be very low. While the frequency 
of light vibrations is measured in the trillions per second that of 
the lowest producing the sensation of light being about 392 trillions, 
those of electrical waves are more often in the thousands. The 
greatest frequency obtained with electrical waves is about 50 bil- 
lions per second, which would give a wave length of about 6 milli- 
meters. Frequencies as low as 500 per second have been dbtained. 
The wave length used in wireless telegraphy varies between 100 and 
1000 meters, being limited, as later shown, by physical con- 
siderations. 

The wave length and frequency necessarily depend upon the same 
characteristics, and a change that will vary one will vary the other. 
The wave length produced by an organ pipe when blown depends 
upon the length of the pipe, and similarly it may be said that the 
wave length of an electrical discharge depends upon the " electrical 
size " of the apparatus that furnishes the discharge. 

The analogy of sound waves in an organ pipe to the electric waves 
transmitted along a conductor may be carried still further, experi- 



886 Naval Electricians' Text Book 

ment showing that the nodes and loops of the sound waves find 
their counterpart in electric waves. Keferring again to the form, 
of the wave, the points a, h, and c represent the nodes or points of 
no vibration, or rather points at which the resultant of all the vibra- 
tions is zero, and 0.0 loops, points representing the position of 
maximum vibration, or where the particles have the freest motion; 
and in the electric waves, the points of greatest potential. At the 
nodes, in the electrical waves, there is the least potential. 

An organ pipe closed at one end, when blown, gives as its funda- 
mental note, a sound represented by a wave such that there is a 
loop at the blown or free end, and a node at the other, the closed 
end. This is shown in Fig. 386, where the dotted line shows the 
form of the wave. 



Fig. 386. 

In this wave, the amplitude varies from nothing at the closed end 
to a maximum at the open end, and it depends upon the energy 
expended in forcing the air into the pipe. The wave length, how- 
ever, and consequently the frequency depends on the length of the 
pipe, whether the force of the air be strong or feeble. The ampli- 
tude produced by a single strong puff of air, might be obtained by a 
series of more feeble puffs constantly directed into the tube, if 
these feeble puffs are rightly timed with each other. 

If a conductor with one end insulated while the other end is 
kept at a constant potential by being connected to earth, is free to 
vibrate electrically, under the action of an electric force, it is 
found that there is a node of zero potential at the earthed end and 
a loop of maximum potential at the free end, while the wave length 
will depend upon the length and capacity of the conductor. From 
the nature of the phenomenon producing electric vibrations, it is not 
possible to obtain a single electric blow sufficient to produce the 
required amplitude, and recourse must be had to a series of light 
blows well timed with each other and to the natural frequency of 
the conductor to produce the desired result, as in the case of the 
light puffs of air properly timed in the organ pipe. 



Principles of Wireless Telegraphy 887 

It is noted that the full wave length as shown in Fig. 386 would 
be four times the length of the pipe, and so in the case of the 
electrical oscillating conductor, the length of the conductor is 
theoretically one-fourth of the wave-length produced. 

Aerials. 

An aerial wire or antenna is a name given to the conductor by 
which the electrical oscillations are directed into the ether of the 
atmosphere and is the essential element in all wireless telegraphy. 

If in Fig. 383, the balls of the spark gap >S" are lengthened out 
so that the high frequency oscillatory sparks cannot pass between 
them, the circuit will nevertheless still continue to vibrate electri- 
cally, setting up magnetic fields around it when the induced cur- 
rent is alternating back and forth due to the inductive influence of 
the primary coil T" , and throwing off into space the electromag- 
netic waves, if the source of power is being put at intervals into the 
primary coils V . 

If the lower ball of the spark gap S' is bent around and connected 
to earth, and the upper ball bent around and lengthened vertically, 
we shall have the aerial as universally used for wireless telegraphy, 
the aerial still vibrating electrically, with the lower end earthed and 
the upper end free. 

The action of the electrical vibration, or the 
induced alternating current, in the earthed aerial 
may be best illustrated by considering the spark 
gap S as being directly in the aerial. 

Fig. 387 shows such a case. If now the two sides •/ 

of the spark gap are connected to the opposite I 

plates of a condenser, the upper part is charged to Fig. 387. — Wave 
a high potential and the lower part to zero poten- on Earthed 
tial, that of the earth, and discharge takes place 
across the gap. Just before discharge takes place the upper portion 
of the aerial has a certain capacity with regard to the earth and 
takes a certain charge,* and as the spark has a low resistance, the 
discharge is oscillatory, but much damped, as the energy is rapidly 
radiated. 

The earthed end of the aerial is at zero potential, or there is 



I 

/ 

i 

I 

I 

i 

I 

I 



888 



Naval Electricians' Text Book 



a node of potential at that point. It then follows that there must 
be a loop of potential at the npper or free end, and the funda- 
mental oscillation excited in the whole length of the wire is one in 
which the potential increases all the way up the wire from the 
earthed to the free end, and this wave form is shown by the dotted 
line in Fig. 387. 

The distribution of the current is such that there is a maximum 
current at a potential node and minimum of current at a potential 
loop. 

, ^ The elementary form of the wave would indi- 

/ \ cate that the aerial should be one-fourth of the 

wave length of the oscillation. Owing, however, 
to the inductance in the aerial, experiment shows 
that the length is more nearly equal to one-fifth 
of the fundamental wave length. 

It is not necessary that the aerial should be 
directly connected to the circuit containing the 
spark gap, but it can be connected inductively, as 
shown in Fig. 383 in the elementary transmitter, 
formed as stated, by bending the arms of the 
spark gap S' around, earthing one, and lengthen- 
ing the other vertically. 

Looped Aerials. — A looped aerial is one made 
in the form of a loop with its two ends connected 
to earth, one end through the spark gap and the other through a con- 
denser, as illustrated in Fig. 388. 

These are used in some forms of wireless sets, and present the 
peculiar circumstance that they will radiate for some frequencies 
of oscillation and not for others. If the lower condenser plate is 
not connected to earth, there is no radiation from the loop as a 
whole. Some characteristic forms of aerials are shown in Fig. 389. 



\ 



\* 



-/ 



Fig. 388. 
Looped Aerial. 



Coupling. 

Direct and Inductive Coupling. — Direct coupling consists in 
connecting the aerial directly to some point on the oscillating 
circuit, usually the inductance, another point on the inductance 
being connected to earth. 



Prixciples of Wireless Telegraphy 



889 



Inductive coupling consists in coupling the oscillating circuit 
to the aerial inductively, the secondary of the oscillating trans- 
former being in series with the aerial. 

These are illustrated in Figs. 390-391. 



* ^mm^ 






W^ 



Fig. 389. — Typical Forms of Aerials. 



Open and Closed Circuits. — The closed circuit is that part con- 
taining the spark gap, condensers and inductance, and the open 
circuit is that part containing the aerial with its portion of the 
inductance. 



890 



Naval Electricians' Text Book 



In direct couplings the open and closed circuits have some turns 
of inductance in common, as the turns of the inductance embraced 
between the connections 1 and 2 in Fig. 390. When the common 
turns of the closed and open circuits in directed connected coupling 
are large in number, or the coils of the inductively connected cir- 
cuits are close together, the circuits are said to have a close or 
tight coupling. In this case the energy is radiated very fast from 
the aerial and the oscillations are correspondingly damped. When 
the common turns of the closed and open circuits are few in num- 
ber, or the inductively connected coils are few, the circuits are said 
to have a loose coupling'. In this case, the oscillations are kept up 
more strongly and the radiation from the aerial is less. 



i — i 



Fig. 390.— Direct Coupling. 



I — 1 



3P 



Fig. 391. — Inductive Coupling. 



Each of the closed and open circuits has a natural period of 
vibration, due to its capacity aiui inductance, and when they are 
adjusted to have the same period of vibration, they are said to be 
in tune with one another. 

Though each of the closed and open circuits may be tuned with 
each other before coupling, yet when they are coupled, the resulting 
period is not the same as either, and experiment shows that the 
resulting oscillation has two periods of vibration, and consequently 
two different wave lengths. 

In close coupling, there results two periods of vibration, one 
longer and one shorter than the natural period of either circuit. 

In loose coupling, the resulting two periods more nearly coin- 
cide with the natural period of each circuit. 

The percentage of coupling is the ratio of the difference of the 



Principles of Wireless Telegraphy 



891 



periods of the two waves sent out to the natural period of each 
circuit; or what amounts to the same thing, the ratio of the differ- 
ence in length of the two waves sent out to the natural wave length. 

Detachment of Electromagnetic Waves. 

Let Fig. 392 represent the aerial connected inductively to a closed 
oscillating circuit. 

Just before discharge at the spark gap takes place, all the energy 
is stored in the condenser plates and is electrostatic. At the in- 
stant of discharge, the charges move towards one another as indi- 





Fig. 392. — Detachment of Waves. 



cated by the arrows, 1 — 1, and induce magnetic lines of force in 
the inductance of the aerial, whose direction is perpendicular to the 
direction of the aerial, as indicated by arrows 2 — 2. Due to the 
induction of these magnetic lines of force a current is induced in 
the aerial. These induced currents vary in intensity along the 
aerial and have the greatest value at the earthed end, as at this 
point it has been shown that the potential is least or the rate of 
change of current greatest, and have the least value at the top end 
of the aerial. This moving current or charge carries with it its 
electric lines of strain. There is a lateral pressure in the ether 
tending to keep these lines apart from one another and a tension 
along them tending to shorten them. 



892 Naval Electricians' Text Book 

The result of one single discharge at the spark gap might then 
be graphically represented by the curved lines of electric force or 
electrostatic lines of strain as shown in the figure radiating off 
each side of the aerial. It must be remembered that this condition 
of electric stress is produced in all directions around the aerial, 
making a semispherical surface bounded by the furthest -removed 
electrostatic line of force. Although this surface is represented as 
a spherical ring, it may not be so, the only condition being that 
it is a closed surface. The electrostatic lines are closed through the 
ground, being the result of the common potential. 

The result shown is that at the instant after discharge. The 
reaction immediately follows; the lines of force, both electrostatic 
and magnetic collapse on the aerial, and if there are no more oscilla- 
tions, the lines of force are dissipated, the electrostatic lines closing 
on themselves through the ground and being completely neutralized. 

However, as the closed circuit is vibrating rapidly, the outward 
rushing of the second series of lines takes place before the first can 
entirely collapse and so pushes them, as it were, further along, and 
as they are not entirely collapsed the energy of the succeeding 
oscillation causes the electrostatic lines to be pushed further away. 
The magnetic lines are increasing at the same time. All matter 
possesses inertia and the collapsing lines of force cannot imme- 
diately return owing to the inertia of the imponderable ether. 

Each succeeding oscillation along the aerial finds the electro- 
static surface pushed further and further along until finally it is 
detached from the aerial and travels onward through space as a 
wave form with its two characteristic vibrations at right angles to 
each other. The wave is shown as a semispherical ring travelling 
along over the. ground and directed by it. The lines of vibration 
of the ether particles producing electrostatic induction form meri- 
dians of this sphere or vertical circles and those producing electro- 
magnetic induction are at right angles, and form circles of lati- 
tude, or horizontal concentric circles in a section of the ring. 

These waves are propagated in all directions and the direction 
of propagation is at right angles to the directions of the two 
vibrations. 

These waves maintain continuous contact with earth and are not 



Principles of Wireless Telegraphy 893 

propagated throughout space and cannot be reflected by the earth 
into space as might be the case if they were completed on them- 
selves independent of the earth. This earth connection also facili- 
tates the transmission of the wave in a direction parallel to the 
earth's surface. The earth guides the waves, allowing them to 
follow its curvature and pass obstacles if they are not too large in 
proportion to the size of the wave. The dimensions of the wave 
increases with the height of the aerial and a big wave will more 
easily overcome a distant obstacle than a small one. The dimen- 
sions do not refer to the length or amplitude of the wave which 
depends respectively on the frequency of the oscillation of the 
aerial and on the energy of the sending apparatus, but to the 
volume, or it might be said, the mass of the waves. The longer the 
waves, the more easily they will flow around obstacles, so that on the 
other side the vibrations are still perceptible, and long wave length 
is a very desirable quality of these electromagnetic waves for suc- 
cessful wireless work. 

PART IV. 
RECEIVING CIRCUITS. 

It has been shown that the wave surface detached from the aerial 
of a sending station proceeds through space as a continually in- 
creasing disturbed mass of ether in which there are two distinct 
lines of vibrations of the ether particles at right angles to each 
other. One set of lines of vibrations (magnetic) are practically 
parallel to and the other (electrostatic) are perpendicular to the 
earth's surface. 

If an earthed conducting wire is held vertical to the earth's 
surface in a region where these waves are travelling the lines of 
force will direct themselves towards it in order to go to earth 
through it, and the higher the aerial the more lines of force it will 
be able to embrace. This conductor will be cut at right angles by 
the magnetic lines of force, which are proceeding as a series of 
horizontal concentric circles, and will induce alternating potentials 
in it. Similarly, a horizontal conductor will be cut by the electro- 
static lines of force and alternating potentials would be induced in 
it. A conductor in any position between the vertical and horizontal 



894 Naval Electricians' Text Book 

positions will be acted upon by the combined action of both series 
of lines of force. 

If this receiving aerial has a natural period of vibration due to 
its capacity and inductance equal to that of the passing waves, the 
amplitude of induced currents will gradually rise, due to the suc- 
cessive impacts of each advancing vibration, the effect of each one 
being added to the preceding one. 

The analogy of this is seen in the ringing of a heavy bell. On 
first drawing the bell rope, the bell may barely move, but a second 
pull rightly timed will cause an increased vibration and soon it may 
begin to swing in its own particular period of vibration, and each 
pull of the rope at the proper time will increase its swing until 
finally the bell rings. The bell then has been rung by a series of 
very light pulls, each correctly timed to correspond to the natural 
vibration period of the bell as it is suspended. 

If the periods of the wave and the aerial are the same, each 
passing wave will add its potential to that due to the preceding 
one and the amplitude of the vibration will soon reach its maxi- 
mum, when the aerial will radiate as much energy as it absorbs. 

To increase the natural frequency of its vibrations, the aerial is 
either connected direct or inductively to a closed circuit in which 
there is both capacity and inductance and in which either may be 
varied. 

The receiving circuit then is similar to the sending circuit, the 
place of the spark gap being taken by the detector, by which the 
vibrations of the closed circuit are made manifest. 

Whatever form of detector is used, it must be sensitive enough 
to respond to the maximum amplitude, or greatest potential, of the 
oscillating circuit. 

The following elementary diagrams show the receiving circuits 
of various forms of wireless sets, and it is noticed they contain 
nothing but the aerial, inductance, and capacity in circuit with the 
detector, which in each case is marked D. 

Some of these present peculiarities, notably the Stone, De Forest, 
and Shoemaker circuits. The circuit of the Stone system is in- 
ductively connected, and the middle circuit, as shown, is called a 
weeding out circuit. This is used to prevent interference when 



Principles of Wireless Telegraphy 



895 



Slaby Arco Massie. 




Shoemaker 




De Forest. 




Stone. 'W//'/ 

Fig. 393. — Receiving Circuits. 



896 Naval Electricians' Text Book 

very close tuning is sought, but can be cut out wnen it is not 
necessary. 

The De Forest and Shoemaker use the loop aerial, the con- 
trolling idea being the setting up of stationary waves in the closed 
circuit, which is grounded. By changing the relative positions of 
the capacity and inductances, the nodes and lopes of the stationary 
wave may be varied so as to produce maximum current or maximum 
potential at the detector, depending on the form used. 

Detectors. 

Each portion of a receiving circuit in a space through which 
electromagnetic waves are passing is subjected to an alternating 
electric force followed by a magnetic force at right angles to it, 
and all wave detectors are devices for detecting the existence of 
these forces. 

The most general forms of detectors may be classified under the 
following heads: Contact, thermal, magnetic, and electrolytic 
detectors. 

Contact Detectors. — The most usual form of contact detector is 
known as a coherer, and there are many patented varieties of this 
device. In its elementary form, it consists of an exhausted glass 
tube, provided with little pistons, which act as terminals for con- 
nection to the receiving circuit, and between which is some form 
of powdered metal. The conduction of powdered metal acts in a 
peculiar manner. A loose heap scarcely conducts electric currents 
at all, owing generally to the want of adhesion of the particles and 
to the resistance of air films between the particles. If an electric 
oscillation occurs near such a coherer, the powder becomes a good 
conductor and the particles cohere, as the resisting films of air are 
broken down by the successive internal discharges from one particle 
of the powder to another, and it will remain a good conductor until 
the continuity of the particles is destroyed by shaking or striking 
them. 

The electromagnetic waves striking the circuit of which the 
coherer forms a part, induces an oscillating current through the 
coherer powder which causes a succession of very minute sparks 
from one particle to another and which produces electrical con- 



Principles of Wireless Telegraphy 897 

tinuity throughout the powder. The coherer is inserted in a local 
circuit with a few cells in series with a relay, and when current 
flows from the local battery through the coherer and relay, the 
attraction of the relay armature closes another circuit which con- 
tains the recording instrument. 

The coherer is used in the Slaby Arco system and is illustrated 
in Fig. 394. 

Detectors of the coherer type are now rarely used in ship instal- 
lation, having given way to other forms and principally to some 
form of electrolytic detector. 

Carborundum Detector. — This wave responsive or wave detecting 
device comprises a body of crystalline silicid of carbon, known 
generally as carborundum. The body of crystals forming the mass 
is composed of carbon and silicon in a chemical combination, form- 
ing what is known chemically as carbid of silicon, or silicid, or more 




w 

Fig. 394. — Slaby Arco Coherer. 

generally as carborundum. It is a highly refractory material, ex- 
tremely hard and is relatively a poor conductor of electricity. 

This substance may be connected in the receiving circuit in many 
different ways, all of which act efficiently as wave detectors. It 
should be interposed between the connecting wire from the aerial 
and the connecting wire to ground. It may be simply interposed 
with the two connecting wires secured to it in any suitable way, 
either by direct contact, or through contact pieces holding the car- 
borundum ; or it may be held between the points of adjusting screws 
which are connected respectively to the aerial and ground. Again 
the carborundum may consist of two pieces, each in connection with 
the connecting wires and resting lightly against each other on 
relatively sharp edges. 

One of the connecting wires may be connected to a piece of 
carborundum, a sharp point of which may rest in an electrolyte, 
such as mercury, or an acid, or an alkaline fluid, while the con- 



898 Naval Electricians' Text Book 

necting wire to the ground is secured to the vessel containing the 
electrolyte, if it is a conductor ; or it may be immersed in the electro- 
lyte or even connected to another piece of carborundum which rests 
in the fluid. 

In all cases, the usual telephone receiver is connected around the 
detector with a battery included in the circuit ; although if the two 
ends of the detector are connected to the ends of a looped aerial, one 
side of which is grounded, the battery may be dispensed with, if 
the telephone receiver is connected to the same points on the aerial. 

Crystalline Detectors. — The carborundum detector is one form of 
many crystalline detectors whose action in cohering or decohering 
is not thoroughly understood. One other form that seems to depend 
upon the resistance of imperfect contacts consists of two crystalline 
minerals, zincite and copper- pyrites. If a piece of copper pyrites 
is secured to the connecting wire from the aerial and a piece of 
zincite to the ground connection, there can be found one degree of 
contact between them which acts as a very perfect detector; the 
usual telephone receiver and battery being connected around the 
contact of the two crystals. 

Thermal Detectors. — One form of detector based on thermal 
action is used in the Fessenden system, although the system as 
applied to ships of the navy uses a form of electrolytic detector. 

The principle of this thermal detector depends upon the prop- 
erty of metals presenting a higher electrical resistance as their 
temperature increases. It consists of a silver wire bent into the 
shape of a V having a diameter of .05 mm. with a core of platinum 
.0015 mm. in diameter. The lower end of this V is immersed in 
nitric acid, which dissolves the silver for a short length of the 
platinum. The wire is contained in an outer covering of silver, 
which is held in a glass vessel from which the air has been ex- 
hausted, and through which connecting wires lead from the out- 
side and are soldered to the silver wire. 

When the exposed platinum wire at the point of the V is in 
circuit with the electric waves, it heats rapidly, and as rapidly 
cools when the wave ceases. In the same circuit is placed a battery 
and a telephone, the variation of the resistance producing variations 
in the telephone current which produces sounds more or less pro- 



Principles of Wireless Telegraphy 



899 



longed, according to the train waves, and these are longer or 
shorter as the wave trains sent out by the sending circuit or of 
greater or shorter duration. 

Magnetic Detectors. — This form of detector is based on the prin- 
ciple that rapidly alternating currents permanently modify the 
•magnetization of a magnetized steel bar. The electric waves strik- 
ing such a magnetized bar induces currents in a conductor wound 
around it which may be made manifest in several ways. After a 
change in the magnetization due to the impact of the oscillating 
current, it must be remagnetized before it is in a position to again 
be affected. The general principle is exhibited in Fig. 395. 

The magnetized substance is a bundle of very fine steel wires, 
insulated one from another. Around this is wound the aerial, 
with the other end connected to earth. Over this is a coil of a 




Fig. 395. — Magnetic Detector. 



great many turns of fine wire to which a telephone receiver is con- 
nected. Due to the demagnetization of the bundle of wires cur- 
rents are induced in the coil which traverse the telephone and 
owing to their alternating character produce sounds, of a duration 
depending on the length of wave train. 

The magnetism is restored by a revolving horseshoe magnet 
which constantly remagnetizes the bundle of wires. 

This form of detector was devised by Marconi but has not been 
used in ships of the Navy. Its practical working form is different 
but the principle remains the same. 



900 



Naval Electricians' Text Book 



Electrolytic Detectors. — This form of detector depends upon 
the power of electric oscillations to affect the polarization of small 
metallic surfaces immersed in an electrolyte. The general prin- 
ciple in most detectors of this type is explained in a description of 
the Schlcemilch Detector. This is illustrated in Fig. 396. 

A primary cell is arranged to consist of two electrodes, one of 
platinum, A, and the other lead, B, and the electrolyte of dilute 
acid. The platinum anode A is made very fine, both in its length 
and diameter, being about .01 mm. long and .001 mm. in diameter, 
and arranged so that the point just touches the surface of the 
electrolyte. 



v-onr^ 




Fig. 396. — Schlcemilch Detector. 



This electrolytic cell is placed in series with another primary 
battery with a slightly higher E. M. F. and included in the same 
circuit is a resistance coil and telephone receiver. This primary 
battery sends a small current through the electrolytic cell and 
soon 'polarizes the electrodes; that is oxygen gas is liberated from 
the acid by the current and the bubbles collect on the small plati- 
num anode. The resistance of the gas so increases the total re- 
sistance that the current from the primary battery soon falls to zero, 
or practically so. 

If now the electrolytic cell is connected to a circuit in which 
electric oscillations are set up, these oscillations momentarily de^ 
polarize the surface of the platinum anode, which suddenly reduces 



Principles of "Wireless Telegraphy 901 

the resistance of the cell. Current then as suddenly flows from the 
primary battery, and through the telephone in which a sound is 
heard, its duration depending upon the impact of long or short 
trains of waves. These sounds are then of shorter or longer dura- 
tion, corresponding to the dots and dashes of the telegraphic code, 
the length of train wave made by the length of time the sending 
key is kept in contact. 

The electrolytic cell as practically used varies in details, some 
using platinum cells as in the Fessenden type, others glass cells 
as in the De Forest type. It is usual to seal the fine wire of the 
anode in a glass tube, leaving just the minutest portion of the 
surface exposed. In this form the tube may be immersed in the 
electrolyte, and the care necessary to keep the fine point adjusted 
to the surface of the liquid is eliminated. 

In order that the potential of the primary battery may be ad- 
justed to the proper value for just polarizing the anode in the 
electrolytic cell, its terminals are connected through a potentio- 
meter or variable resistance whereby the current can be accurately 
controlled. All forms of wireless sets used on ships of the Navy 
are so connected with the exception of the Shoemaker type. 

The Shoemaker type of electrolytic cell does not require an 
extra primary battery, but uses its own current to depolarize itself. 
It consists of a fine platinum wire sealed in glass as the positive 
electrode and amalgamated zinc as the negative electrode, both dip- 
ping into an electrolyte of 20 per cent solution of sulphuric acid. 
The telephone receiver is simply shunted across the terminals of the 
detector. 

Detector Circuits. 

Eeferring to Fig. 393, in which elementary diagrams of various 
forms of receiving circuits are shown, the detector in each case is 
marked D. The detector circuits shown in Fig. 397 may be con- 
sidered the complete diagram of the detector circuits. 

Inductance and Capacity of Receiving Circuits. 

The object of inductance and capacity in the receiving circuit is 
to give it a certain period of vibration in order that it may respond 



902 



Naval Electricians' Text Book 



to a certain frequency or wave length of the sending circuit. Ai 
the natural frequency depends upon both of these factors, and for 
the purposes of changing the wave length, it is usual to fit the 
receiving circuits with both variable inductances and capacities. 

Variable Inductances. — Variable inductances are usually of the 
step-by-step or roller form. A convenient form of step-by-step 
inductance is made by making a cylindrical coil of insulated wire 



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wound on glass, or some form of hard rubber with one point on 
each turn bare. A sliding contact moves across these points, 
giving as many adjustments as there are turns in the coil. 

Step-by-step inductances are also sometimes made with plug 
steps, giving a limited number of changes. 



Principles of Wireless Telegraphy 903 

Roller type of inductances may be of the single-roller or double- 
roller type. In the single-roller type a bare wire is wound on a 
groove cut in an insulating cylinder, and against this wire is pressed 
a sliding contact. By revolving the cylinder any fraction of its 
length can be put in circuit. In the double-roller type a bare 
conductor runs from one insulating cylinder to another. On one 
cylinder the turns of the wire are insulated and on the other they 
are in contact, so any desired length can be added to the circuit. 

Variable Capacities. — These are generally of the step-by-step or 
sliding type previously described. 

Variable capacities in receiving circuits are more essential than 
variable inductances, as a strong pronounced natural period can 
only be obtained by a large inductance, leaving the variation in 
wave length to be accomplished by the variable capacities. If the 
wave length ia to be very greatly increased it can be done by adding 
a large inductance to the aerial at some point that will not inter- 
fere with the inductance necessary for the absorption of power in 
the closed circuit. 

PART V. 
WAVE METERS. 

In any circuit containing resistance, capacity, and inductance, 
if the resistance is small in comparison with the inductance, the 
number of oscillatory vibrations per second such a circuit will 
follow will be given by the formula : 

1 

where K = capacity in farads, 

L = inductance in henries, 
and n = number of oscillations per second. 

Therefore, knowing K and L for any circuit, which values can be 
found by independent measurement, n may be calculated, from 
which the wave length may be found from the formula : 

V = n\ or k = — , 
n 

where X = the wave length, in the same units as V, which is the 

velocity of the electromagnetic waves or the velocity of light. 



904 Naval Electricians' Text Book 

Thus the length of wave corresponding to the natural vibra- 
tion period of any circuit containing inductance and capacity may 
be found. Wave meters are circuits containing these factors, with 
provision for varying their values and for each combination of 
which the wave length has been calculated. 

Donitz's Wave Meter. — An inspection of this device (Fig. 398) 
will show a closed circuit containing inductance and capacity in 
series. The inductance is in the form of a ring with plug terminals 
by which it is connected to the condenser. This last occupies the 
main space devoted to this meter and consists of several semi- 
circular metallic sheets, parallel to one another and fixed; while 
an equal number of similar semicircular sheets are movable around 
a vertical axis, and so arranged that they can be fixed to slide more 
or less into the spaces between the fixed sheets, thus constituting a 
condenser of variable quantity. These plates are contained within 
a circular vessel which is filled with oil. 

The knob that moves the plates is provided with a pointer which 
moves over a scale indicating the wave length for the given in- 
ductance and the capacity of the condenser corresponding to the 
position of the plates at that time. The instrument is provided 
with three separate inductance coils of values 2.8, 12.1, and 50 
microhenries, and there are three scales provided, one to be used 
for each of these coils. 

The indicating apparatus shown on the left consists of a very 
small spiral of platinum sealed in an air thermometer, and con- 
nected inductively to the main circuit. 

When the circuit is vibrating in its natural frequency, the great- 
est current is induced in the platinum spiral which is heated and 
the air thermometer then registers its maximum value. 

Slaby's Helix Wave Meter. — This form of wave meter depends 
upon the principle that if a helix of uninsulated wire is held in the 
hand and the other end held near a circuit in which electric oscil- 
lations are taking place, the length of the helix can be altered 
until the stationary oscillations excited in it are of the same fre- 
quency as those in the circuit under test. The wave length will 
then be four times the length of the helix. 

The practical instrument is made of an insulated copper wire 



906 Naval Electricians' Text Book 

wound in a close spiral on a glass tube J inch in diameter. The 
lower end of the copper wire is in connection with a metal handle 
attached to the glass tube while the upper end is in connection 
with a fluorescent sheet. This is formed of a small sheet of paper 
covered with crystals of barium platino cyanide with gold-leaf in a 
fine state of division rubbed on the surface. This prepared paper 
is then inserted in the upper end of the tube and held by a stopper. 

A metal rod is provided which is connected to an earthed wire. 
When the end of the tube containing the fluorescent paper is held 
near the circuit in which the oscillations are taking place and the 
earthed rod is moved along the spiral, there will be a point in 
which the glow in the prepared paper is greatest. At that point 
the wave length is read on the scale opposite the metal rod. 

Fleming's Wave Meter. — This form of wave meter also de- 
pends upon the establishment of stationary waves upon a helix 
brought near an oscillating circuit. Its general construction is 
illustrated in Fig. 399. 

The inductance consists of an ebonite tube with a helical groove 
cut on it, in which is wound bare copper wire whose ends are se- 
cured to collars on the ebonite tube. Parallel to this helix is 
fixed a sliding tubular condenser. This consists of inner and outer 
tubes of brass with a tube of ebonite between them. The outer 
tube has a collar h at one end to which is attached an ebonite handle 
h. A movement of this handle moves also a collar K on the in- 
ductance and carries a pointer which moves over a scale 88. One 
end of the inductance helix is connected to the inner tube of the 
condenser through the bar L X L 2 L S . A vacuum tube V, preferably 
one filled with rarefied neon is connected with one end of the inner 
condenser tube and the other end should be connected to earth, 
when measuring wave lengths. 

To measure the wave sent out by an aerial, the handle h is moved 
until the vacuum tube glows most brightly and the scale reading 
will be the wave length. 

The form of wave cannot be plotted by this meter as there are no 
means of determining the relative brightness of the glow, but it 
will only show the length of the two waves radiated by the aerial. 

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908 Naval Electricians' Text Book 

also be used to measure small inductances and capacities, one read- 
ing of the scale showing the oscillation constant, ^/KL, expressed 
in centimetres. 

Hot Wire Ammeter. — This instrument is for use in the open cir- 
cuit and measures directly the current in the aerial, and to be 
accurate the whole current should pass through the working wire 
of the instrument. As its name implies it measures the heat 
generated in the aerial, and the heat generated acts to expand a 
conductor which moves a pointer over a scale indicating the number 
of amperes flowing. If the pointer moves off the scale, its termi- 
nals are shunted by suitable resistances whose values are known. 

When the closed and open circuits have the same frequency a 
maximum reading will be obtained on the ammeter, but it will not 
in any way indicate the wave length or degree of coupling of the 
two circuits, though it will show the difference of energy radiated 
dependent upon the tightness or looseness of the coupling. 

Pierce Wave Meter. — The Pierce Wave Meter is very similar in 
design to the Donitz Meter. The place of the air thermometer is 
taken by a telephone receiver and it is fitted for measuring both 
long and short waves, and when used with the former, there is 
included in the circuit an extra inductance coil of fine wire. 
When the frequency of the meter and oscillating circuit are in 
tune, the humming noise produced in the telephone receiver is a 
maximum, and a slight change from complete resonance will de- 
stroy the sound. 

The wave meter can be used as a sender by disconnecting the 
telephone receiver and substituting in its place a small spark gap, 
which can be actuated by a small spark coil. 

PAET VI. 
TUNING. 

By tuning or syntonizing is meant the operation of connecting 
the different circuits of a wireless outfit so that they shall all vibrate 
in the same period, or adjusting the closed and open circuits of 
the sending and receiving circuits to the same wave length. 

There are two conditions necessary to insure the tuning of two 



Principles of Wireless Telegraphy 909 

stations with one another; the sending apparatus should radiate 
waves of well-defined period and but slightly damped, if at all, 
and the frequency of vibration of the different circuits should be 
capable of easy adjustment. 

Between two stations tuned for the same wave length it is pos- 
sible to signal with sending apparatus of much less power and to 
receive with apparatus of less sensibility than if they were not so 
tuned. 

The different circuits are tuned by means of any of the standard 
wave meters previously described, the operation consisting in set- 
ting the pointer opposite the desired wave length and then bring- 
ing the circuit under test in syntony with it by changing its variable 
factors. Most sending circuits have fixed capacity and variable 
inductance, while in receiving circuits, the opposite is the case. 
If variable inductance is needed in a receiving circuit, it can be 
placed where it will not affect the mutual induction of the closed 
and open circuits. 

The question of wave length is one dependent on the possible 
length of aerial with due consideration of sufficient inductance for 
proper coupling. The greater the wave length the more power can 
be used, and it has been shown that long wave length is of ad- 
vantage in passing around obstacles when sending over land. Four 
hundred and twenty-five meters has been adopted as the standard 
wave length for ships of the Navy. 

The sending circuits are usually tuned first and the closed and 
open circuits are tuned separately. 

To Tune the Closed Sending Circuit. 
By Donitz's Wave Meter. — Disconnect the closed circuit from the 
open circuit, if it is directly connected. Set the pointer that 
moves the variable capacity of the meter to the desired wave length, 
and connect one of the inductance coils to its terminals. Bring the 
inductance coil of the meter parallel to the plane of the inductance 
of the closed circuit and close to it, a foot or so, and arrange so 
that the circuit produces a clear, bright spark of moderate length: 
This will induce oscillating currents in the meter circuit and pro- 
duce heat in the thermometer coil and the thermometer will indi- 



910 Naval Electricians' Text Book 

cate a certain reading. Now vary the inductance of the closed 
circuit until the thermometer gives its maximum reading. The 
two circuits will then be vibrating in tune, and the wave length of 
the closed circuit will be the same as that of the meter. Note the 
number of turns of inductance in circuit. 

By Slaby's Wave Meter. — Hold the end of the spiral at which 
the fluorescent paper is placed to the circuit in which oscillations 
are taking place and move the earthed rod along the spiral until it 
is opposite the desired wave length. Then vary the inductance in 
the closed circuit until the brightest glow in the fluorescent paper 
is produced. At that time the closed circuit has the wave length 
indicated by the rod. 

By Fleming's Wave Meter. — Move the handle that changes both 
the inductance and capacity until the pointer is opposite the de- 
sired wave length. Bring the copper bar which joins one end of 
the inductance spiral to the inner tube of the condenser parallel to 
the plane of the inductance coil of the closed circuit. With a clear, 
bright spark as before, start the oscillations of the closed circuit 
which act inductively on the circuit of the meter. Vary the in- 
ductance of the closed circuit until the vacuum tube glows most 
brightly, at which time the circuit has wave length indicated by the 
pointer. 

By Pierce's Wave Meter. — Set the pointer moved by the handle 
of the variable capacity to the desired wave length. Produce the 
spark in the closed circuit as before and bring the inductance coil 
of the meter near the inductance of the circuit under test. Place 
the telephone receiver to the ear and vary the inductance of the 
closed circuit until the maximum sound is produced in the tele- 
phone. When this is the case the two circuits are in tune. 

To Tune the Open Sending Circuit. 

Disconnect the closed and open circuits in direct-connected sets 
as before, and arrange a small spark gap in the aerial in series 
with it and the ground, and to the terminals of this spark gap add 
a small spark coil, or connect them to the terminals of the in- 
duction coil and have just enough energy to give a clear, bright 
spark. 



Prixciples of Wireless Telegraphy 911 

If the aerial is inductively connected, remove the inductance to 
first find the natural period of the aerial. 

By Donitz's Wave Meter. — Bring its inductance coil parallel to 
the aerial. For this purpose a special coil of one turn is furnished 
for insertion inside the wave meter inductance, and connect this in 
series with the aerial. As the capacity of aerials is comparatively 
small, this is done to bring the inductance coil of the meter very 
close to the aerial. Now vary the capacity of the meter until the 
maximum reading is obtained, when the natural frequency of the 
aerial will be indicated by the pointer. 

At the same time, it is well to insert the hot wire ammeter in 
the aerial and note and record its reading for the natural period 
of vibration. 

By Slaby's Meter. — With everything as before, approach the 
fluorescent end of the helix and move the rod along it until the 
maximum glow appears. The reading then opposite the movable 
rod is the wave length due to the natural period of the aerial. 

By Fleming's Meter. — With the previous arrangement bring the 
upper bar parallel to the lower part of the aerial and about 3 or 4 
inches from it. The terminal of the vacuum tube which is con- 
nected to the outside of the sliding condenser should be connected 
to earth. Move the handle along the inductance coil until the 
maximum glow appears in the vacuum tube when the reading oppo- 
site the pointer will be the natural period of the aerial. 

By Pierce's Wave Meter. — Approach the inductance coil of the 
meter to the oscillating aerial and close to it, and with the tele- 
phone receiver to the ear, move the handle of the condenser. When 
the maximum sound is heard, the pointer indicates the natural 
period of the aerial. 

After the natural period of the aerial has been obtained by any 
of the above means, the wave length can be brought to tune with 
the closed circuit by setting the indicators to the proper wave length 
in the different forms of meters, and adding a sufficient number of 
turns of the common inductance in direct-connected sets or of the 
aerial inductance in inductively-connected sets to give the same 
frequency as the wave meters, being indicated by the maximum 
readings of the meters, according to their construction. 



912 Naval Electricians' Text Book 

Wave Forms. 

By the use of Donitz's Wave Meter it is possible not only to obtain 
the maximum reading of the thermometer, at which time the wave 
length is indicated, but other readings may be obtained with other 
positions of the index of the variable capacity, and in this way a 
series of points may be obtained through which curves may be 
drawn giving the wave form. 

For these curves, wave lengths or indications of the capacity 
index, are used as abscissae and thermometer or hot wire ammeter 
readings, as ordinates according to some convenient scale, and 
curves are drawn through the points so plotted. They can be 
plotted for the natural length of aerial; for the aerial with its 
inductance; and for the natural closed circuit. . 

A study of these curves will in a general way indicate the sharp- 
ness of their resonance and the distribution of energy. 

Coupled Circuits. 

After the closed and open circuits have each been tuned sepa- 
rately, they are then coupled together. If the wave length is 
tested after the circuits are coupled, it will be found in general 
that there are two points of maximum -intensity indicated by the 
wave meters, indicating two wave lengths, though as a matter of 
fact, the wave curve shows one wave with two humps. If the 
curve is plotted with wave lengths as abscissae, and either ther- 
mometer or hot-wire ammeter readings as ordinates, one hump 
will be found to have a greater and the other a less value than the 
wave length to which one of them separately was tuned. 

The percentage of coupling is the ratio of the difference between 
the two maxima to the natural wave length of each circuit, and if 
closed coupling is desired, the mutual induction between the two 
circuits is then varied until the two maxima are at the desired 
points. If very loose coupling is desired, the mutual induction is 
varied until but one maximum is indicated by the wave meter and 
this will be very near the natural wave length of each circuit when 
not coupled. 



Principles of Wireless Telephony 913 

To Tune the Receiving Circuit. 

Keceiving circuits should have strong natural periods of vibra- 
tion, and this can be obtained by large inductances, leaving the 
tuning to be accomplished by variable capacities. Adding large 
inductances to the aerial for receiving to increase the natural period, 
does not have the bad effect of adding it for sending, as it will 
receive waves of almost any length, but will radiate only feebly if 
its period is far removed from its natural period. If the receiving 
circuit has high resistance, the open circuit should be adjusted to 
the wave length of the sender. However, adding inductance to the 
closed receiving circuit beyond a certain value, is of no value, as 
no increase of the natural period will serve to strengthen the signals. 

As close coupled senders radiate two waves, one longer and one 
shorter than the natural period of each, it is possible to adjust the 
receiving circuit in tune with either wave, but experiment shows 
that best results are obtained when both the open and closed re- 
ceiving circuits have the same natural period as the sending cir- 
cuits and have the same coupling. The longer wave has the 
lower frequency and has the least damping and consequently greater 
amplitude or intensity, and if the receiving circuit is to be tuned 
with only one wave, it would be more advantageous to syntonize 
with the longer one and disregard the other. 

Tuning by Wave Meters. — Of the various forms of wave meters 
described, only two, the Donitz and Pierce can be used for tuning 
receiving circuits. 

The Pierce Wave Meter is supplied with a special spark gap. 
The telephonic receiver is removed and the spark gap supplied is 
put in its place. This attachment has a coil in its base of the 
proper inductance to replace the telephone. The spark gap should 
be actuated by a small spark coil by attaching the secondary of 
the spark coil to the two sides of the wave-meter spark gap which 
should be opened not more than .1 to .2 of an inch. 

The index on the capacity is then set to the proper wave length 
and the meter used as a sender. It should be placed about three 
meters from the aerial. Conditions of resonance of the meter with 
the receiving circuit will be indicated by the maximum sound in 



914 Naval Electricians' Text Book 

the receiver telephone and can be effected by changing the in- 
ductance in the receiver tuning coil. 

The Donitz Wave Meter may be used in the same manner as a 
sender, by arranging a spark gap in the circuit and actuating it by 
a small spark coil. 

It is usual to calibrate one of the elements of receiving circuits. 
They have either fixed inductance with variable capacity, or vice 
versa. For one given value of one element, the other may be 
marked in wave lengths according to its varying values. Thus, in 
the Stone set, which consists of three coils, inductively connected, 
the second is calibrated. All have fixed inductances and variable 
capacities. With the fixed inductance, the frequency or wave 
length is calculated from different capacities, and the resulting 
wave length is marked on the handle which moves the condenser 
plates. 

In such cases, if the values of the variable elements are known 
for different positions of the controlling devices, the tuning can be 
effected without wave meters, as the different circuits will be in 
tune with each other when the product of the inductance and 
capacity in each is the same. 



CHAPTEE XXXVII. 
PRINCIPLES OF WIRELESS TELEPHONY. 

Wireless telephony differs from wireless telegraphy in that it 
transmits articulate sounds while telegraphy limits itself to the 
transmission of inarticulate sounds, which are made the basis of a 
code by which words may be sent or received in the form of mes- 
sages. In telegraphy the sound produced in the telephonic receiver 
is that due to a certain number of vibrations which fall within the 
range necessary for the production of sound and the frequency or 
period of the vibrations is not important; but for the reproduction 
of articulate sounds, there must be a very wide range of frequencies 
to correspond to the immense number of vibrations of which speech 
is composed. 

The range of frequencies for the production of sound vary be- 
tween 16 double vibrations per second and 40,000 double vibrations, 
the former giving the lowest audible sound and the latter the highest 
musical note. For the average man's voice, the number of double 
vibrations per second is 128, and for the average woman's voice, 
the number is from 256 to 512. 

The efforts of the earlier experimenters in wireless telephony 
were directed to the idea of using the connection afforded by the 
earth. In general, the scheme consisted in stretching two parallel 
wires, one at each station, the extremities being taken to earth. In 
one of these wires was inserted a microphone with a battery of dry 
cells, and in the other a telephone which reproduced words pro- 
nounced at the microphone. 

Although such schemes did not require a connecting wire between 
stations, yet the total length of the parallel wires at the two sta- 
tions was required to be about the same length as the distance 
between the stations. Such a telephonic circuit has been in opera- 
tion for some years in England, where communication is held 
between the lighthouse on the Isle of Skerry and the coast-guard 
station of Cemlin, a distance of about three miles. 



916 Naval Electricians' Text Book 

Theoretical Principles. 

In 1878, two American physicists, Graham Bell and Sumner- 
Tainter discovered that a beam of light that had been made inter- 
mittent, falling upon a thin sheet held against the ear, gave a 
sound, the number of whose vibrations is equal to the number of 
interruptions in the source of light. By making the duration of 
the intermissions longer or shorter, the duration of the sound pro- 
duced was longer or shorter. Any source of light whose intensity 
can be varied can be used in this experiment but the distance to 
which the phenomena can be manifested is increased by using a 
receiving circuit composed of a selenium resistance in series with a 
telephone and battery. 

Crystalline selenium has the remarkable property of being a much 
better conductor of electric currents when illuminated by a beam of 
light, and of increasing its conductivity with the intensity of the 
light. If such a resistance is exposed to a luminous radiation of 
variable intensity, the variations of intensity will cause variations 
in the resistance of the selenium and consequently in the battery 
circuit which will vary the current flowing through the telephone 
and which will in turn emit sounds corresponding to the changes 
in the quantity of light. 

If the electric arc is used as the source of light, variations in 
intensity may be produced by certain properties it possesses when 
arranged as discovered by Duddel, and known as Duddel's sing- 
ing arc. 

Duddel's Singing Arc. — If an alternating current of small in- 
tensity be placed in a favorable condition in respect to a continuous 
current which is feeding an electric arc, the arc itself will emit a 
sound. At the same time equal oscillations are produced in the 
light of the arc. If the alternating current is set up in the circuit 
of a microphone by speaking in it, the oscillations produced in the 
arc can be received by a selenium receiver placed at a distance, and 
the luminous oscillations will cause the spoken words to be repro- 
duced in the telephone in the receiving circuit. 

The alternating current may act on the circuit which feeds the 
lamp in a shunt circuit from the feeding circuit, or it may be in 
another circuit which acts inductively on the feeding circuit. 



Principles of Wireless Telephoxy 917 

Fig. 400 shows the connections for the first condition. 

R is a resistance wound on a soft-iron core, around which passes 
the whole of the current feeding the arc. From the ends of the coil 
is connected a microphone M. R can be so adjusted that a battery 
in connection with M will be unnecessary. As the microphone is 
spoken into, the variations in resistance caused by the sound waves 
changes the current feeding the arc and the light of the arc will 
vibrate in rhythm with the diaphragm of the microphone and simi- 
lar vibrations will be set up in the selenium receiver and the words 
will be reproduced in the telephone of the receiving circuit. 




\TJ WJJ\ 

M 

Fig. 400. — Duddel's Singing Arc. 

Explanation of the Singing Arc. — In the phenomenon of the 
singing arc, the variation of the feeding current caused by the super- 
position of the current due to the microphone develops greater heat 
in the arc, as the heat is proportional to the square of the current. 
Similar variations in the volume of the incandescent gases forming 
the arc are caused by this variation in heat, and these variations 
in volume are those which generate sound vibrations in the air, 
reproducing the vibrations in the microphone, and causing the arc 
itself to sing. 

Duddel's Circuit. — In this circuit, the extremities of the arc are 
joined with a circuit comprising a capacity and inductance as shown 
in Fig. 401. 

D is a generator supplying continuous current to the arc L, joined 
to the extremities of which is a circuit composed of a capacity C 
and inductance I". Such a circuit has a natural period of electrical 
vibration depending on the values of the capacity and inductance. 



918 



Naval Electricians' Text Book 



If certain conditions are satisfied at the instant when the circuit of 
the arc is made, the condenser becomes charged and discharged with 
a frequency depending on the oscillation period of the circuit, 
thereby producing alternating currents which overlap the con- 
tinuous current feeding the arc and cause it to vibrate with a period 
equal to that of the alternating current and the rest of the circuit. 
If this frequency lies within the range of percepticle sounds, the arc 
admits a musical note. 




Fig. 401. — Duddel's Circuit. 



If the arc is made between the poles of a powerful magnet, either 
permanent or an electromagnet, both the frequencies and intensities 
of the alternations are much increased. 

This oscillating circuit does not radiate its energy, and to pro- 
duce radiation, the circuit may be inductively connected through an 
air transformer to an open circuit which may be made an aerial 
similar to that of wireless telegraphy, one end being grounded. 
This transformer is shown at 1,1', where / is the primary of the 
transformer inductively connected to the secondary V which forms 
part of the aerial, the lower end of which is grounded. 

The portion of the circuit LCll" is known as Duddel's circuit. 
This circuit has very little damping, and almost perfect resonance 



Principles of Wireless Telephony 919 

may be obtained in two circuits, which is very powerful in case of 
coincidence of frequency of vibration, but which falls off rapidly 
when the resonance is less perfect. 

In such an arrangement as shown in Fig. 401 under certain con- 
ditions there would be a continuous radiation from the aerial of a 
definite period and amplitude. If the amplitude of these waves 
could be varied by the vibrations due to the voice, the train of 
radiated waves would consist of all the elements necessary to the 
transmission of speech. 

Such a condition is effected by introducing a microphone in the 
aerial between the secondary and the ground. If this is now 
spoken into, the constant radiated energy of the aerial will have 
superimposed on it the varying energy caused by the changes in the 
microphone resistance and consequently the radiated waves will 
have all the varying amplitudes caused by the sounds of the voice 
speaking against the diaphragm of the microphone. 

Electromagnetic Waves. 

From the preceding explanation it will be seen that the waves 
radiated from the aerial of a wireless-telephone sender differ from 
those of a wireless-telegraph sender in that the amplitude of each 
wave in a wave train from the former varies according to the im- 
pulses that have been given to it by the voice and consist of all the 
various irregularities of amplitude that are characteristic of sound 
waves, while those from the latter are probably of nearly equal 
amplitudes. Aside from this difference the two series of waves are 
practically the same, with the same characteristic vibrations of the 
ether at right angles to each other, and are propagated through space 
in the same manner, guided by the earth through which the lines of 
force are completed. 

Receivers. 

The receiver necessary to reproduce every fluctuation of the 
energy of the transmitter may be any of the various forms of auto- 
matically restoring responders using a telephone receiver, such as 
the imperfect contact coherer, magnetic detector, electrolytic de- 
tector, the carborundum or silicon detector. The one said to be the 



920 



Naval Electricians' Text Book 



most sensitive and to give the clearest quality to the reproduced 
tones is the " Audion," or hot-gas responder, devised and patented 
by Doctor De Forest, and which can also be used in wireless 
telegraphy. 

Audion. — The Audion consists of a device for detecting feeble 
electrical currents or oscillations, particularly such as are developed 
in wireless telegraph or telephone systems. " The Audion itself com- 
prises a receptacle, which may be partly exhausted, including a 
sensitive, gaseous conducting medium, and in which are two elec- 
trodes of suitable conductors. 




Fig. 402. — Connections of Audion. 



The elementary connections of the Audion to the wave intercepter 
and the signal-producing device are shown in Fig. 402. 

In the figure / represents the wave intercepter, or the aerial of the 
telegraph or telephone installation, connected with the earth at E. 
A is the Audion with its two electrodes C and D inclosed within it 
and which contains air partly exhausted, or a gas containing com- 
pounds of the halogens or halogen salts, or mercury vapor. C is 
an ordinary incandescent lamp filament and is connected to a bat- 



Principles of Wireless Telephony 921 

tery B' . The electrode D may be any suitable conductor, as a plate 
or disc of platinum. 

The gaseous medium inclosed between C and D is rendered sensi- 
tive to electrical oscillations by the radiation of heat from the 
electrode C which is heated by the battery B'. 

The passage of electrical oscillations across the gap between the 
electrodes alters the conductivity of the gas in the gap, and con- 
nected in series with this gap is a circuit containing a telephone T 
and battery B". When the electric oscillations pass across the gap, 
the change in the conductivity of the gas produces current variation 
in the circuit containing the battery B", causing the telephone, T, 
to respond. The telephone may be connected either in series or in 
shunt with the electrodes. The aerial may be connected to either 
electrode, in which case the other must be connected to earth. 

The voltage to be impressed on the electrodes C and D by the 
battery B" depends on the nature of the gas between the electrodes 
and upon the degree of exhaustion within the receptacle, a voltage 
from twenty-five to one hundred and ten volts is sufficient, the 
needed voltage decreasing with the degree of exhaustion. 

This device is free from all the adjustments required of those 
detectors that depend for their operation upon variation of resist- 
ance of an imperfect electrical contact or counter E. M. F. of a 
polarization cell. 

De Forest Wireless Telephone. 

This system designed by Dr. De Forest and made by the Kadio 
Telephone Company of New York has been installed on many of 
our ships of war. The system is based upon the modulation by a 
telephone transmitter of trains of electromagnetic waves of rela- 
tively high frequencies. These waves are generated in a way, fol- 
lowing the methods shown by Thomson and Duddel, such that the 
frequency of the oscillations becomes so great as to enter the range 
of Hertzian waves, at which frequencies, energy begins to be radi- 
ated into space from the aerial wires. 

The direct-current arc is used in connection with an alcohol 
flame, special arrangements being made to render the arc quiet 
and free from hissing or popping sounds which would render the 



922 Naval Electricians' Text Book 

reception of speed more or less obscure. To adapt an arrangement 
of the low-potential arc to wireless transmission of speech it is neces- 
sary to secure a spark frequency exceeding the tones used in speech, 
and if this frequency be higher than that, having for example, over 
40,000 vibrations per second, the pitch of the aerial vibrations pro- 
duced by the spark becomes so high as to make them inaudible to 
the human ear, and the articulation and clearness become perfect. 
The 40,000 double vibrations correspond to a wave length of 

— ? ' — = 7500 metres. 

The variation of the amplitude of the radiated waves is accom- 
plished by placing a microphone transmitter in the earth lead of 
the aerial between an inductance and the ground; this inductance 
being inductively coupled with the closed oscillating circuit. The 
microphone is placed near the ground where the high-frequency 
currents are maximum and the potentials are the least. 

The general elementary diagrams of this system is shown in 
Fig. 403, and the sending circuit can be studied in connection with 
the Duddel circuit shown in Fig. 401. The receiving circuit can 
be readily understood from the description of the Audion pre- 
viously given. 

The diagram of connections is shown in Figs. 404 and 405, and 
with the help of those of Fig. 403 will be readily understood. 

In late installations, the appliances are assembled in a compact 
form in a transporting case which admits of their use in the chart 
house or emergency cabin or on the bridge. 

Instructions for Tuning and Operating De Forest Radio-Telephone 

Apparatus; 

The following directions are furnished by the makers, the Eadio 
Telephone Company, New York. The lettering refers to Fig. 405 : 

Transmitter, Type C. 
Source of Power. — This should be from 200 to 250 volts direct 
current. From 2 to 5 amperes give best results. If motor gen- 
erator is used give to it the care any such machine properly 
demands. 



Principles of Wireless Telephony 



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Naval Electricians' Text Book 




Fig. 404. — Diagram of Connections. De Forest Wireless Telephone Set. 



Principles of Wireless Telephony 



925 



vVv -./ RHEOSTAT TO ANTENNA LOOP 

f V i * . , ft OSCILLATING CIRCUIT SWITCH If] LISTENING 




TRANSMITTER 



SECONDARY P. C. 



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TO TRANSMITTER 



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PRIMARY P.C. 



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TUNER 




AU.DION 



Fig. 405.— Connections of Apparatus. De Forest Wireless Telephone Set. 



926 Naval Electricians' Text Book 

Kheostat with pilot lamp in shunt thereto must be connected in 
circuit, preferably between transmitter and choke coil. One choke 
coil must be in each leg of circuit. Positive lead goes to upper 
binding post behind lamp (lettered P+). This leads to the rear 
or copper-arc electrode. 

Negative lead goes to lower binding post (lettered P — ). This 
leads to the lamp bracket and to the front, or carbon, electrode. 

Arc Oscillator. — The lamp tank should be kept full of denatured 
alcohol, and never allowed to get entirely empty. This is import- 
ant. The tank should be filled full each morning when commenc- 
ing work. 

To facilitate starting oscillator when cold a little alcohol may be 
poured on wick through top of chimney, but this is not advised. 

The opposing faces of the electrodes should be perfectly flat and 
parallel. After several hours' usage, if arc becomes unsteady with- 
draw the carbon electrode from the lamp by turning knob counter- 
clockwise until rack clears the gear. If rough file off the face of 
the carbon with file supplied for this purpose. 

Use no other carbons than those supplied with transmitter. 

To Start Oscillator. — Close the main line switch. Turn feed 
knob on lamp until electrodes make contact and pilot lamp lights, 
then separate electrodes until pilot lamp glows to half-brilliancy 
Eesistance of rheostat should be nearly all in so that arc is just 
nicely self-sustaining; and once properly set need not be touched 
thereafter. 

The arc is out if pilot lamp is not lit. 

The arc is closed if pilot lamp is full brilliancy. 

Let arc burn until alcohol lamp is well lit, and arc will begin 
to oscillate. 

Listening Key. — This switch must be depressed for transmitting ; 
elevated for listening. 

Glow or Index Lamp. — The little 10-volt lamp directly above 
transmitter arm will glow as soon as arc begins to " oscillate." 

Adjust length of arc until this lamp glows brightly — not neces- 
sarily at its brightest. 



Principles of Wireless Telephony 927 

Tuning the Transmitter. 

Condenser. — Open transmitter door and cut in sections A, or B, 
or A and B of condenser, according to length of wave desired. 

Section A contains 3 plates. 

Section B contains 4 plates ; A and B 7 plates. 

Both condenser plugs must be on corresponding pegs of the jack, 
i. e. both on A (right and left sides respectively), or both on B, 
or both on AB. 

Primary Spiral. — The flexible lead and clip can be attached to 
any bared convolution of this spiral as desired. The outer turn of 
spiral is recommended as giving longest wave lengths and steadiest 
operation of the arc. 

Secondary Spiral. — With listening key depressed and index lamp 
burning, now move the slide knob on front of transmitter slowly up 
and down until hot-wire antenna gives maximum deflection. The 
secondary, or antenna, circuit is then in tune with primary circuit. 

Fine adjustment of tuning is obtained by moving primary spiral 
towards or from secondary spiral, but loose coupling is recom- 
mended. 

The arc should not be opened too wide, or ammeter needle will 
fluctuate rapidly, indicating that arc is unstable and liable to go out. 

Talking. — The small switch on transmitter arm is thrown to its 
upper position for talking. Hold mouth close in front of mouth- 
piece and talk directly therein. Speak clearly and distinctly, not 
too rapidly. Talk loudly but do not shout. 

Do not thrust the lips into the mouthpiece, as this renders the 
words muffled and indistinct. 

The megaphone will increase the action on the transmitter. In- 
vert it and speak directly into the larger end. 

Listening in. — Keep the head phones on the head, and at end of 
every sentence throw up listening key with fingers or thumb of 
right hand, to assure yourself that the other party hears you 
clearly and answers you. 

Never attempt to talk unless key is down and glow lamp lit. 

With a little practice two speakers will almost unconsciously de- 
press this key when talking and raise same when expecting a reply, 



928 Naval Electricians' Text Book 

so that two-way conversations can be carried on almost as rapidly 
as over the wire telephone. 

Microphone. — The buttons become warm but not injuriously so. 

It is well to occasionally tap upon the case of the microphones 
with screw-driver to shake up the carbon granules. 

If your own transmission is good you should hear this tapping in 
your own head receiver very clearly. If you cannot hear this 
(your receiver of course being in proper adjustment) try adjusting 
the arc, etc., until you do. The larger the ammeter reading (if 
steady) the better the transmission. 

A frying or scratching sound in the adjacent receiver accompanies 
the properly oscillating arc. 

Receiving Apparatus. 

Audion Receiver Lighting Voltage. — The Audion filaments are 
made for 3 volts — 2-cell storage battery only. Higher voltages 
must not be used, otherwise the filament will soon burn out. 

Eheostat should be all in when first connecting up a newly- 
charged storage battery, i. e. have rheostat index arm turned as far 
in a counter-clockwise direction as possible. 

Audion filament should be bright, but not excessively incan- 
descent. 

Battery " B." — The telephone battery is inside Audion case. 
The switch arms for same are on right-hand side of case. 

The circular switch cuts in three cells per point. 

Lower switch cuts in one cell per point. 

Switch arm must not cover two points at one time, as this short 
circuits the cells. 

Adjust voltage until you hear the signals (from some distant 
station) at their maximum intensity. 

If this voltage be made too high the blue cathode arc is seen in 
the bulb, and sensitiveness is diminished. 

Once adjusted both rheostat and " Battery B " switches should 
remain set. These should not be thrown back to zero when sending. 
Breaking the Battery A (lighting) circuit also interrupts the tele- 
phone circuit, and it; is sufficient merely to break this A circuit 
when sending with a powerful spark, in order to prevent the 



Principles of Wireless Telephoxy 929 

Audion's responsiveness from being even momentarily interrupted 
by said spark. 

Always cut off storage battery by means of switch on left side of 
receiver box when Audion is not in use. Do not forget this. 

As the storage battery runs down cut rheostat resistance out 
gradually. Keep a duplicate battery always charged in readiness. 

If voltmeter be connected across storage battery see that voltage 
is never too high for the Audion filament. 

Double-Filament Audions. 

The double filament has twice the life of a single filament. When 
first filament has burned out unwrap the small bare copper wire 
which is coiled around the glass neck of the bulb and tuck it under 
the little brass clip which is soldered on to the outside cap of the 
stem ; or twist this copper wire around the wire stub soldered to this 
cap. This will put the second filament in the circuit, and Audion 
is then to be replaced in its receptacle inside the box. 

Connect the red wire lead to small binding post marked red ; the 
green lead to binding post marked green. 

Tuning the Receiver. 

" Pancake " Tuner. — Have the two tuner pancakes approximately 
i inch apart at the start. Connect the " Impedance " binding posts 
one to one lead from the transmitter box and the other to the earth 
lead. These binding posts are lettered I and E respectively. Con- 
nect the other lead from the transmitter to center binding post of 
primary p. c. (lettered A) and the earth lead to one of the other two 
binding posts on the p. c. (lettered or I) . Connect Audion bind- 
ing posts marked A and E to the two binding posts on end of tuner 
box marked VC. The lead to C leads also over to the binding post 
(lettered A) on the secondary p. c. Connect the flexible lead 
from the fixed condenser inside the tuner box to the binding post 
on the secondary p. c. (lettered or 7) . 

Adjust the two swinging arms and the " Impedance " arm to 
give maximum sound in telephone receiver from distant transmit- 
ting station. 



930 Naval Electricians' Text Book 

Then adjust capacity of variable condenser (VC) in slmnt across 
the two Audion leads, to further increase signals, or cut this VC 
out entirely, according to length of wave to be received, etc. 

Finally, or to cut out interferences, separate the p. c's. by a 
distance giving the loudest signals, thus " loosening the coupling." 

The tuning by means of the contact arms now becomes sharper. 
For undamped oscillations from the radio-telephone transmitter 
tuning may be made exceedingly sharp. 

A little practice and manipulation will enable one to cut out 
powerful interferences, and to " bring in " the desired station much 
more loudly than seems possible on first attunement. 

For special work the extra variable condenser (VC) at the back 
of tuner box is to be connected in any part of the tuner circuit 
where it may be needed; for example, in the antenna lead to pri- 
mary p. c, or in series in the Audion, or secondary, circuit. 

The Audion has an excessively small electrostatic capacity, hence 
tuning with it is extremely sharp. 

By adjustment of Battery B on Audion it is possible under some 
conditions to effect a separate method of tuning auxiliary to the 
usual method. But once attuned to a given radio-telephone trans- 
mitter this tuner and Audion receiver require little attention. 

Antenna. — The " Loop " antenna should always be used in re- 
ceiving. Connect one end thereof to each of the antenna leads 
coming out from the top of the transmitter case. 

Earth Lead. — This lead should be as short as possible from 
" Earth " to the hot-wire ammeter and thence to lower binding post 
(marked E) on transmitter case. Eun a spur lead from earthed 
side of ammeter to the " Impedance " binding post lettered E, and 
to binding post marked A on primary p. c. of tuner. 

To Telegraph. 

The two extra leads from transmitter arm must be connected to 
the two rear binding posts on the " Chopper " telegraph box (let- 
tered M). Connect three cells of dry battery in series to the two 
left-hand binding posts (lettered B) . Now throw the small switch 
arm on transmitter arm to its lowest contact. 

By means of the small screw-driver adjust (when necessary) the 



Principles of Wireless Telephony 931 

" chopper " contact in bottom of box (reached through the single 
hole in top of chopper box) until the hot-wire ammeter needle's 
throw is reduced to about one-half its normal reading when the tele- 
graph key is held closed. 

The Morse sending key may be operated at the highest possible 
speed. This chopper telegraph may be also used for calling pur- 
poses. 

Eemember always to throw the transmitter arm switch up for 
talking. 

Care of Apparatus. 

It is very important that all parts be kept clean and dry, espe- 
cially when exposed to salt sea air and moisture. Keep doors of 
hood closed as much as possible, and all metal parts wiped dry, 
or with cloth dampened in " 3 in 1 " oil. 

If moisture gets in telephone cords it tends to short circuit same, 
reducing the received signals. 



INDEX. 



The numbers refer to pages, and in nearly all cases, the sub-heads of 
the index refer to matter in the text given in bold-faced type. 



Acceleration 

C. G. S. unit, 10 
example, 12 
explanation, 10, 11 

Accessories, wiring 
care, 843 

Activity 

C. G. S. unit, 16 
law of maximum, 
274 



motors, 273, 



Aerials 
forms, 889 
looped, 888 

wireless telegraphy, 887 
wireless telephony, 918 

Age 

effect on candle-power, incan- 
descent lamps, 585 

Air 

diamagnetic, 114 
table of insulators, 51 

Alcohol 

diamagnetic, 114 

Alloy, alloys 

German silver, 38 
melting point, 39 
platinoid, 38 
use of, 35 

Alternating currents 
capacity, 436, 437 
comparison with direct, 442 
definition, 872 
graphic representation, 433, 

434, 435 
impedance, 435 
principles, 425 
self-induction, 428 
variation of E. M. F., 425, 426 



Aluminum 

annealed, resistance, 38 
electrochemical series, 54 
melting point, 39 
paramagnetic, 114 
table of conductors, 34 

Always 

instructions for operation, 863 

Ammeter, ammeters 
calibration, 702 

connections, 703 
care in connecting, 679 
care in using, 679 
checking with testing set, 709 
hot wire, 908 

measurement of current, 698 
measurement of resistance 

with voltmeter, 700 
measurement resistance shunt 

windings, 720 

Ammunition, chain hoist 
care of, 855 

location safety devices, 855 
lubrication, 855 
motor, 298 

armature, 299 

armature bearings, 298 

brake, 300 

brush rigging, 299 

commutator, 299 

field coils, 299 

magnet frame, 298 

panel, 300 

pole pieces, 298 

test, 299 
operation, to start, 856 
to stop, 856 
cautions, 856 
solenoid brake, 855 

Ammunition hoists 
circuits, 813, 825 

wiring, 826 
turret, 405 



934 



Index 



Ampere 
hours, 92 
lost, 183 
milli, 18 

practical unit of current, 18 
shunt, 683 
turns, 130 

Ampere hours, 92 
secondary cells, 82 

Ampere shunt 
connection, 684 
explanation, 683 

Ampere turns, 177 

Amplitude 

alternating current, 872 
definition, 427 

Angle 
lag, 432 
lead, 433 

Annunciator, annunciators 

faults, 776 

systems, 771 

types, 775 

fire alarm, 775, 776 
non-water-tight, 775-776 
water-tight, 775 

wiring, 771, 772, 773 

Anode 

primary cells, 55 
secondary cells, 75 

Antennae (see Aerials) 

Antimony 

paramagnetic, 114 

Appliances 
care of, 869 

non-water-tight, 649, 654 
wiring, conduit, boxes (s< 

Boxes) 
wiring, molding, 651 

Applicability 

variable speed gear, 396 

Arc, arcs 

deflector for controllers, 343 
multiple, 46 

grouping of cells, 64 

resistance, 46, 47 



Arc, arcs — Cont'd 

oscillator, De Forest wireless 

telephone, 926 
singing, Duddel's, 916 

explanation, 917 
stoppers, wireless telegraphy, 
879 

Arc, arcs electric 
carbons, 598 
counter E. M. F., 597 
electrodes, 596 
form and temperature, 596 
lamps, 599 

requirements, 599 
production, 595 
regulation, 598 
resistance, 597 

search-light, regulation, 599, 
600 

Arc lights 

candle-power, 611 

carbons, 598 

counter B. M. F., 597 

electrodes, 596 

enclosed, description of, 609, 

610 
flaming, 613 
general principles, 595 
mercury vapor, 613 

Area 

C. G. S. unit, 10 

Armature, armatures 
balance, 459 
bearings, rotary compensator, 

449 
boat-crane motor, GE-800-E, 

306 
chain ammunition-hoist motor, 

299 
characteristic curve of current, 
469 
connections for obtaining, 

469 
instructions for making, 470 
cores, 170, 171 
core, type M. P. generator, 6-32- 

80, 229 
determination of E. M. F. 
around, 493 
Joubert's method, 495 
Mordey's method, 495 
Thompson's method, 495 






Index 



935 



Armature, armatures — Cont'd 
disc brake, 359 
electromagnet, 126 
fall of potential around, 497 
fracture, 734 

generator, 100 K. W., 242 
commutator, 243 
core, 243 
spider, 242 
windings, 244 
generator, service, 220, 221 
generator, type M. P. 6-32-80. 

228, 229 
grounds, 734 

insulation, 100 K. W. genera- 
tor, 245, 246 
binding wires, 246 
flanges, 245 
slots, 245 
winding, 245, 246 
insulation, M. P. generator, 6- 

32-80, 230 
insulation of conductors, M. P. 

generator 6-32-80, 231 
losses, 196 

resistance by comparison of 
deflections, 461 
instructions for test, 462 
resistance method, of motor 

control, 267 
resistance of windings, 722 
rotary compensator, 450 
Sturtevant blower motor, 310 
turret-turning motor, 302 

Audion, 920 

connections, 920 
voltage, 928 

B 

controllers, 347 

Backing strip, 656 

Balancer 

connections, 607 
explanation, 607 

Band brakes, 483 
Base 

attachment, incandescent 
lamps, 583 

Battery, batteries 

" B," De Forest wireless tele- 
phone, 928 



Battery, batteries — Cont'd 

bells and buzzers, 774 

best arrangement and effi- 
ciency, 65, 66, 67, 68 

E. M. F., 58 

economical working, 68 

firing, 72 

primary, 53 

quarters and office calls, 769 

resistance by testing set, 708 

resistance primary cells, 60 

resistance working, 61, 62 

ringing, ship telephone switch- 
board, 792 

secondary, 75 

service testing set, 691 

statistics, 74 

talking, ship telephone switch- 
board, 792 

types, primary, 70 

typical secondary, 75 

Battle lantern, 662 

Battle order 

cable, 764, 766 
circuits, 768, 810 

transmitter and indicator, 
810 

Battle service, 629 

Battleship 

distribution of current, 638 

Bearings 

armature, chain ammunition- 
hoist motor, 298 

boat-crane motor, GE-800-E, 
305 

care, 858, 860 

compression grease cups, 859 

grease, 860 

main, Gen. Elec. Co. Form H-l 
engine, 527 

main, tandem-compound en- 
gine, 511 

self-oiling, 858 

sight feed, 859 

Sturtevant blower motor, 311 

Bell 

telephone receiver, 744 
call, 774 

non-water-tight, 774 

water-tight, 775 
call, circuits, 769, 770 



936 



Index 



Binnacle light, 666, 667 

Bi-polar 

telephone receivers, 744 

Bismuth 

paramagnetic, 114 

Blake 

telephone transmitter, 741 

Blinker signal, 669 

Blowers 

motor, Sturtevant 
armature, 310 
bearings, 311 
brush rigging, 313 
commutator, 311 
description, 308 
field coils, 310 
magnet frame, 309 
pole pieces, 309 

Board, distribution, 574 
connections, 576, 577 
explanation, 575 

Boat cranes 

electrical equipment, 411 

diagram of connections, 413 

electrical connections, 412 
gear, care, 856 

lubrication, 856 
revolving motor, GE-800-E, 303 

armature, 306 

bearings, 305 

brush rigging, 308 

commutator, 308 

field coils, 305 

magnet frame, 303 

pole pieces, 305 

Body, the 

table of partial conductors, 34 

Boosters 

charging current, secondary- 
battery, 86 

Box, boxes 

5-ampere receptacle, 650 

interior fittings, 653 
5-ampere switch and recepta- 
cle, 650 
interior fittings, 653 
25-ampere switch and recepta- 
cle, double pole, 650 
interior fittings, 653 



Box, boxes — Cont'd 

5-ampere switch, single pole, 
650 
interior fittings, 653 
25-ampere switch, double pole, 
650 
interior fittings, 653 
50-ampere switch, double pole, 
650 
interior fittings, 653 
conduit wiring 
distribution 
8-way, 648 
12-way, 648 
feeder, 648 

four (4) way junction, 648 
main junction, 648 
three (3) way junction box, 

648 
water-tight, 648 

l^-inch conduit, 648 

l^-inch conduit, 648 

1-inch conduit, 648 

%-inch conduit, 648 

%-inch conduit, 648 

connection, 830 

care, 868 
feeder junction for double con- 
duit, 650 
junction, conduit wiring, 650 
molding wiring 

5-ampere receptacle, 652 

interior fittings, 653 
5-ampere switch, single pole, 
651 
interior fittings, 653 
25-ampere switch, double 
pole, 652 
interior fittings, 653 
50-ampere switch, double 
pole, 652 
interior fittings, 653 
100-ampere switch, double 

pole, 652 
50-ampere switch, double 

pole, double throw, 652 
5-ampere switch and recepta- 
cle, 652 
interior fittings, 653 
25-ampere switch and re- 
ceptacle, 652 
interior fittings, 653 
25-ampere switch and re- 
ceptacle, double pole, 652 
interior fittings, 653 



Index 



937 



Box, boxes — Cont'd 

feeder junction, 651 

interior fittings, 653 
main junction, 651 

interior fittings, 653 
three (3) way junction, 651 
interior fittings, see main 
junction, 653 
stowage, fire-control tele- 
phones, 820 
tilting, variable speed gear, 
394 

Bracket light, 657 
double, 657 
single, 657 

Brackett's cradle 
description, 484 
measurement of output, 485 

Brake, brakes 

automatic, for boat cranes, 414 
band, 356 

chain ammunition-hoist motor, 
300 

care, 855 
disc, 357 

annular rings, 359 

armature, 359 

coil, 360 

compression springs, 360 

discs, 359 

electromagnet, 359 

frame, 359 

magnetic core type, 361 
electric for controller, rotary 

compensator system, 386 
horsepower, formula, 483 
mechanical, 483 

arm type, 483 

band type, 483 
solenoid, 355 

solenoid, chain ammunition- 
hoist motor, 408 
windings, 361, 362 

Branches, 630 

Brass 

conductor, 34 
conduit, 655 
use, 35 

Breaks 

test by magneto, 711 



Bridge, Wheatstone, 686 
theoretical, 687 

Bridging connections 
telephone, 747 

Bronze 

conductor, 34 
melting point, 39 
phosphor, conductor, 34 
use, 35 

Brush, brushes 
care, 838 
carrier, 100 K. W. generator, 

250 
generator, 100 K. W., 250 
method adjusting, 251 
position yoke, 250 
generator, service, 224 
generator, type 6-32-80, 233 
holders, generator, type 6-32- 

80, 233 
holders, service generators, 

225, 226 
lead, motors, 267 

relation to speed, 267 
renew, generator, type 6-32-80, 

234 
rocker, generator, type 6-32-80, 

234 
sparking, 460 
ventilation sets, 857 

Brush rigging 

boat-crane motor, GE-800-E, 

308 
care, 839, 840 
chain ammunition-hoist motor, 

299 
rotary compensator, 450 
Sturtevant blower motor, 313 
turret-turning motor, CB-24, 

302 

Buckling 

plates, secondary batteries, 86 

Building up 

generators, 178, 189 

Bulb 

incandescent lamp, 582 
exhausting, 582 

Bulkhead fixture, 657, 659 



938 



Index 



Bunker fixture, 657, 659 
overhead, 657, 660 

Bus 

feeder, 630 

Bushes 

conduit fittings, 655 

Buttons, push, 830 
Buzzers, 774 

water-tight, 775 

Cable 

classification, 764 

battle order, 764 

controller, 764 

intercommunication, 764 

night signal, 764 

powder division, 764 

range indicator, 764 
interior communication, 762 

Calibration 

ammeters, 702 

connections, 703 
instruments, 702 
voltmeters, 703 

connections for different 
voltages, 703 

Call bell 

batteries, 774 
circuits, 768, 769 

quarters and office calls, 769 

voice-tube calls, 769 
simple circuit, 769 
water-tight, 775 
wiring, 770, 771 

Calling apparatus 
telephone, 747 

Calls 

batteries, 769 
office, 769 
quarters, 769 
voice tube, 769 

Calorie 

C. G. S. unit of heat, 16 
relation to joule, 27 

Candle-foot 
definition, 591 



Candle-power 

arc light, 611, 612 
comparison, 584 
effect of age, 585 
incandescent lamps, 584 
maintenance, 590 
mean spherical, 585 

Capacity 

alternating currents, 436 

C. G. S. unit, 30 

dependent on impedance, 438 

example, 30 

explanation, 873 

practical unit, 30 

receiving circuits, wireless 

telegraphy, 901 
relation to quantity, 436 
secondary cells, 81 
variable, 903 

Capping, 656 

Carbon, carbons 
arc light, 598 
circuit breakers, 350 
electrochemical series, 54 
specific resistance, 37 
table of conductors, 34 
use, 35 

Carbonizing 
filaments, incandescent lamps, 
580 

Cardboard 

use, 52 

Care of electric plant and acces- 
sories 

appliances, 869 

bearings and lubricants, 858 

boat-crane gear, 856 

brushes, 838 

rigging, 839, 840 

chain ammunition hoists, 855 

circuit breakers, 844 

commutator, 836, 837 

connection boxes, 868 

controllers, 846 

diving lantern, 868 

dynamo room, 842- 

engines, 840, 841, 842 

fixtures, 870 

fuses, 845 

generating sets, after stopping, 
832 

generating sets, starting, 834 



Index 



939 



Care of electric plant and acces- 
sories — Cont'd 
generating sets, stopping, 835 
night signal set, 867 
rheostats, 846 
search-lights, 865 
storerooms, 870 
switches, 864 
truck lights, 868 
turret ammunition hoists, 854 
turret- turning system, 850 
ventilation sets, 857 
wiring accessories, 843 

Cast iron 

melting point, 39 

CB-15 

type of motor, 293 
exploded view, 294 

CB-25 

longitudinal section, 297 
type of motor, 295 

ammunition hoist, 305 

exploded view, 296 

CB-27 Form B 

type of motor, 300 
motor assembly, 301 

CB-32 

type of motor, 303 
exploded view, 304 

CB-34 

type of motor, 308 
exploded view, 306 

Ceiling fixtures 
Commercial, 661 
No. 1, 660, 661 
No. 3, 661 

Cell, cells, primary 
definition, 55 
E. M. P., 58 
grouping, 62 

problems on, 69 
Leclanche, 70 

chemical action, 71 
multiple grouping, 64 
multiple series grouping, 65 
resistance, 60, 61 
resistance working battery, 61 
series grouping, 63 
silver chloride, testing set, 689 
statistics, 74 
typical, 56 



Cell, cells, secondary 
capacity, 81 
charging, 79 

chemical action in forming, 78 
chloride, 82 
discharging, 78 

chemical action, 80 
Edison, alkaline, 83 
elements, 76 
Faure, 77 
forming, 77 
output, 81 
pasted, 77 
Plante, 12 
regulation, 83 
reversal, 77 
section, 77 
series and parallel charging, 

. 84 
types, 82 

Center feeders, 632 

Centimetre 

C. G. S. unit of length, 10 

C. G. S. system of units 
capacity, 30 
current, 18 
derived mechanical, 10 

acceleration, 10 

area, 10 

velocity, 10 

volume, 10 
E. M. F., 18 
energy, 14 
force, 12 
heat, 16 
inductance, 31 

magnetic field, 17 

magnetic pole, 16 
power, 15 
work, 13 

Chain ammunition hoist (see Am- 
munition hoist, chain) 

Characteristics 

general, service generators, 217 
table, incandescent lamps, 588 

Characteristic curves (see Curves) 

Charging, secondary cells, 80 

parallel, 85 

series, 84 ■ 



940 



Index 



Chemical action 

discharging secondary cells, 80 
forming secondary cells, 78 
Leclanche, 71 

Chlorides, double 

effect, 72 

Chlorine 

electrochemical series, 54 

Circuit, circuits 

counter B. M. F., 92 
coupled, 12 

percentage, 912 
detector, 902 
divided, 93 
Duddel's, 917, 918 
forms of inductive, 144, 145 
laws of divided, 95 
lighting, 628 

battle service, 629 

lighting service, 629 
magnetic, closed, 125 
magnetic, laws, 130 
magnetic, open, 125 
magnetic, typical, 131, 132 
motor, 629 

open sending tuning, 910 
problems on divided, 99, 100, 

101, 102 
protection, 639 

circuit breakers, 643 

fuses, 639, 640 

calculation for size, 640, 
641 
receiving, tuning, 913 
receiving, wireless telegraphy, 

893, 894 
search-light, 628 
sending, wireless telegraph 

closed, 890 

direct connected, 888 

inductively connected, 889 

open, 889 

tuning, 909 
sending-, wireless telegraphy, 

elem. diagrams, 877 
simple, 89, 90 
simple typical, 91 
temperature, coefficient, 44 
weeding out, 894 

Circuit breaker, breakers 
carbon break, 349 



Circuit breaker, breakers— Cont'd 
care, 844 

type M. L., 844 

type M. Q., 844 
general description, 349, 643 
inspection, 863 
location, 645 
magnetic blow-out, 349 
Navy Standard Panel Type U. 

S., 330 
type C, 354 
type M. L., 352 

care, 844 
type M. Q., 350 

care, 844 

Circular mil 
definition, 614 
relation to square mil, 614 

Closet system of wiring, 631 

Clutch 
magnetic, rotary compensator 

system, 383 
safety, gun-loading equipment, 

403 

Cobalt 
paramagnetic, 114 

Coefficient of 

mutual induction, 149 
permeability, 115 
resistance, temperature, 40 
self-induction, 145, 146, 430 
susceptibility, 115 
temperature, a circuit, 40 

Coherers, 896 
Slaby Arco, 897 

Coil, coils 

disc brake, 360 

induced E. M. P. in closed, 156, 

157, 158 
induction, 150, 151 
for creating electric oscilla- 
tions, 152 
repeating, telephone, 756 
testing set 

resistance, 688 
winding, 688 

Commercial 
efficiency of generators, 194 



Index 



941 



Common battery system 
circuits, 750 

switchboard, 753, 754, 755 
telephone connections, 749 

Commutation 

act of, 161, 162, 163, 164, 165, 
166 

Commutator, commutators 

armature, service generators, 
223 

armature, typo M. P. generator, 
6-32-80, 231 

boat-crane motor, GE-800-E, 
308 

care, 836, 837 

chain ammunition-hoist mo- 
tor, 299 

connectors, type M. P. genera- 
tor, 6-32-80, 231 

rotary compensator, 450 

service testing set, 692 

Sturtevant blower motor, 311 

turret-turning motor, 302 

Compass, 107 

Compensator 

rotary for turret training, 377, 
380 
commutating switch, 380, 

386 
controller, 384 
magnetic clutch, 383 
starting panel, 383 

Compensator, rotary 
description, 449 
armature, 450 
armature bearings, 449 
brush rigging, 450 
commutator, 450 
field coils, 450 
frame, 449 
pole pieces, 449 
series field shunt, 450 
tests, 451 

Compound, -ing 

connecting machines in paral- 
lel, 210 
generator as motor, 272 
generator, 100 K. W., 249 
generator, long shunt, dynamo 
equations, 205 



Compound, -ing — Cont'd 

generator, short shunt, dyna- 
mo equations, 2CI 
generators, 188, 189 

characteristic curves, 470 
connections, 471 
instructions, 471 
comparison of terminal volt- 
age, 191 
curve, 189 
methods of, 269, 270 
motors, 269, 270 

Condensers 

De Forest wireless telephone, 

927 
wireless telegraphy, 881 
plate form, 881 
variable, 882 

Conductivity 

definition, 46, 94 
specific, 46 
unit, 46 

Conductor, conductors 

armature, service generators, 
222 

correction for copper, 41 

definition, 34 

double, insulation, 619 
diving lamp, 620 
plain, 619 
silk, 619 

effect of increase on E. M. F., 
428 

electrical interior communica- 
tion, 763 

insulation armature service 
generator, 222 

insulation armature generator, 
6-32-80, 223 

partial, 34 

single, insulation, 618 

table good, 34 

twin, insulation, 618 

uses, 34 

Conduit 
brass, 655 
fittings, 655 

couplings, 655 

couplings, reducing, 655 

elbows 90°, 655 

nipples, 655 

outlet elbows 90°, 655 



942 



Index 



Conduit— Cont'd 

outlet elbows 45°, 655 

plugs, 655 

unions, 655 
flexible, 655 

size, 655 
steel, 655 

wiring appliances, 648 
wiring installation, 636 

Connections 

apparatus, De Forest wireless 

telephone set, 925 
balancer, 607 

chain ammunition hoist, 407 
commutator, service generator, 

222 
controller, rotary compensator 

system, 378 
cross, armature cores, service 

generator, 222 
diagram, boat cranes, 413 
diagram, De Forest wireless 

telephone set, 924 
diagram whip hoists, 411 
electrical, boat cranes, 412 
electrical, deck winches, 416 
electrical, desk fans, 421 
electrical, generator and motor 

field control, 369, 370 
electrical, motors for doors and 

hatches, 423 
electrical, Ward-Leonard sys- 
tem, 365, 366 
elementary, De Forest wireless 

telephone set, 923 
elementary, elevating equip- 
ment, 398 
elementary, turret ammunition 

hoists, 405 
gun-loading equipment, 401 
gun-elevating equipment, 398, 

400 
mechanical, boat cranes, 412 
mechanical, deck winches, 416 
motor generator turret turn- 
ing, 373, 376 
shunt motors, 265 
whip hoists, 410 

Connection boxes, 830 

Connections and circuits 
service testing set, 692 



Connection rod 

engine, Gen. Elec. Form H-l, 

524 
engine, tandem-compound, 510 

Connectors 

commutator, service generator, 

222 
commutator, 6-32-80 generator, 

231 

Contact 

resistance imperfect, 49 

Control 

armature resistance, 267 
automatic motor, 338, 339 
field resistance, of motors, 268 
generator and motor field for 

turret turning, 370 
Leonard system of motors, 281, 

282 
motor, in general, 277 
motor generator for turret, 376 
motor, theory, 256 
panel, 285 
rheostatic, 279 
series motors, 279 

reverse, 279 

start, 279 
shunt motors, 280 

reverse, 280 

start, 280 

stop, 280 

Controller, controllers 

ammunition hoist 12-inch, 406 
care, 846 

adjustment of fingers, 847, 
848 

operation, 849, 850 
classes, 346 

B, 347 

P, 348 

R, 346 
deck winches, 416, 417 
description 

arc deflector, 343 

blow-out magnet, 343 

cap plate, 344 

contact fingers, 342 

cylinder, 340 

developed, 345 

frame, 340 

handle, 344 

star wheel, 344 



Index 



94:3 



Controller, controllers — Cont'd 
developed R-28, 347 
directions for operating turret, 

852 
directions for operating turret 

ammunition hoist, 854 
gun-loading equipment, 401, 

402 
inspection, 862 

P-10 generator and field con- 
trol, 371 
P-13-A rotary compensator sys- 
tem, 381, 382, 383 
contact ringers, 385 
cylinder, 384 
electric brake, 386 
field connections, 385 
frame, 384 
shaft, 384 
terminals, 386 
R-62 boat cranes, 413 

Converters 
rotary, 452 

Copper 

annealed, resistance, 38 
annealed, specific resistance, 37 
constituent of German silver, 

35 
diamagnetic, 114 
electrochemical series, 54 
hard drawn, resistance, 38 
hard drawn, specific resistance, 

38 
melting point, 39 
table of conductors, 34 
uses, 34 

Cord 
bell, 763 

Cord circuits 

telephone switchboards, 752 

Core, cores 

armature, 170, 171 

armature, service generator, 

220, 221 
armature, generator 100 K. W., 

243 
armature, generator 6-32-80, 

229 
field, 100 K. W. generator, 244 
losses in generators, 196 



Cory & Son 

ship telephone switchboard, 

789, 790, 791 
telephone, non - water - tight, 

type B-l, 783, 785 
telephone, non - water - tight, 

type F, 785, 786 
telephone receiver, 779, 780 
telephone, transmitter, 778, 779 
telephone, water-tight, type 

A-l, 780, 781 
terminal connections, 782 
telephone, water-tight, type 

C-3, 784, 785 

Cotton 

table of insulators, 51 

table of partial conductors, 34 

use, 51 

Coulomb 

practical unit of quantity of 
electricity, 18 

Counter E. M. F. 

circuit, 92 
motor, 261, 262 
problems, 92, 93 

Coupling 
close, 890 
direct, 888 
inductive, 889 
percentage, 890, 912 
tight, 890 

Couplings 

conduit fittings, 655 
reducing, 655 

CR Form G Motor 

assembly, 307 

Cradle, Brackett's 
description, 484 
measurement of output, 485 

Cranes (see Boat cranes) 

Crank shaft 

engine, Gen. Elec. Form H-l, 

523 
engine, Gen. Elec. Form H-2, 

534 
engine, tandem-compound, 511 

Crater 
arc, 596 



944 



Index 



Current, currents 

alternating, principles, 425 
C. G. S. unit, 17, 18, 155 
charging, 436 

curves of E. M. F., 437 
conductors, 34 

continuous, transformers, 444 
curves and rate of change, 429 
direct, comparison with alter- 
nating, 442 
direct, induced, 138 
distribution, battleship, 638 
distribution, gunboat, 637 
eddy, 171, 172, 195 
E. M. F. and power curves, 440 
induced, direction, 138 
inverse induced, 138 
magnetic field in coiled con- 
ductor, 121, 122 
magnetic field in straight con- 
ductor, 115, 116 
measurement, 698 

ammeter, 698 

resistance and voltmeter, 698 

without opening circuit, 698 
oblique, 121 
parallel, laws, 118 
phase in rotary converters, 454 
practical unit, 18 
reversal, due to induction, 147, 

148 
wattless, 441 

Curve, curves 

applied E. M. F. in alternating 

currents, 431, 432 
current and rate of change, 429 
E. M. F., 158, 159, 427 
E. M. F. after commutation, 

167 
E. M. F. before commutation, 

167 
E. M. F. due to two coils, 167 
E. M. F. showing superposi- 
tion, 168 
E. M. F., current and power, 

440 
E. M. F. and charging current, 

437 
E. M. F. and resultant E. M. 

F., 432 
losses, separation, dynamo 

electric machines, 489 
magnetization, 465 
connections, 465 



Curve, curves — Cont'd 
instructions, 466 
no-load loss, 489 
resistance and time, 463 
sines, 159, 426 

total E. M. F., 170, 171, 494 
watt, 440 

Curves, characteristic 
armature, 469 
connections, 470 
instructions, 470 
compound generator, 188, 470, 
472 
compound, 471 
connections, 471 
differential, 472 
external, 472 
instructions, 471 
internal, 472 
series, 472 
series generator, 180, 181, 464 
connections for external, 464 
external resistance and ter- 
minal voltage, 182 
magnetization, 465 
connections, 465 
instructions, 466 
total circuit, 464, 465 
shunt generator, 185, 186, 466 
external, 467 

instructions, 468 
internal, 466 

instructions, 467 
total circuit, 468 

Cycle 

definition, 426, 872 

Cylinder, cylinders 

barrel, variable speed gear, 391 

commutating switch, 386 

controller, 340 

controller, rotary comp. sys- 
tem, 386 

engine, Gen. Elec. Form H-l, 
514, 515 

engine, Gen. Elec. Form H-2, 
529, 531 

engine, tandem-compound, 507 

Day 

system motor control, 283, 284 

Deck fixtures, 657, 658 
Deck lanterns, 662 



Index 



945 



Deck winches 
controller, 417 
electrical connections, 416 
mechanical connections, 416 

Definitions 

amplitude, 427, 872 
cycle, 426, 872 
frequency, 427, 872 
period, 426, 872 
phase, 427 
wireless telegraphy 

alternating current, 872 
damped oscillations, 872 
feebly damped, 873 
strongly damped, 873 
electric oscillations, 872 
high frequency alternating 

current, 872 
sustained oscillations, 872 

De Forest system wireless tele- 
graphy 
care, 931 

connection of apparatus, 925 
diagram of connections, 924 
elementary connections, 923 
instructions for tuning, 922 
receiver, tuning, 928 
telegraphing, 930 
transmitter, type C, 922 

arc oscillator, 926 

index lamp, 926 

listening key, 926 

source of power, 922 

tuning, 927 

Design 

direct current generators, 174 

Desk light, 662, 664 

Detectors, wireless telegraphy 
carborundum, 897 
coherer, 896 

Slaby Arco, 897 
contact, 896 
crystalline, 898 
electrolytic, 900 
magnetic, 899 
thermal, 898 

Devices 

motor control, 324 
motor starting, 324 



Diagrams 

connections De Forest wireless 
telephone set, 925 

resistance, 435 

rotary converter, 453 

sending circuits, wireless tele- 
graph, 882 

vector, component and result- 
ant E. M. P.'s, 434 

wiring, water-tight door equip- 
ment, 422, 423 

Diamagnetic substances 
definition, 114 

Dielectric 

strength of electric machines, 
473, 474 

Dielectrics (see Insulators) 
Dip 

magnetic, 109 

Dipper 

interrupter, induction trans- 
former, 880 

Discharging, secondary cells, 80 
chemical action, 80 
series, 85 

Discs 

disc brake, 359 

Distribution of current 
general systems, 637 
battleship, 638 
gunboat, 637 

Divided circuits, 93 
illustration, 95, 96 
laws, 93 

Diving lantern, 667, 668 
care, 868 

Donitz's wave meter 
description, 904 
tuning closed sending circuit, 

909 
tuning open sending circuit, 

911 
tuning receiving circuit, 914 

Doors 

water-tight equipment, 422 
controller, 422 
wiring diagram, 422, 423 



946 



Index 



Draining 










engine, 


Gen. 


Elec. 


Co. 


Form 


H-l, 


516 








engine, 


Gen. 


Elec. 


Co. 


Form 


H-2 


530 









Drop fixture, 657, 658 

Drop in potential, 622 
examples, 623, 624, 625 
problems, 627 

Duddel 

circuit, 917, 918 
singing arc, 916 
explanation, 917 

Dynamo 

study, 456, 457 

Dynamos (see Generators) 

Dynamo electric machines, 444 
general tests, 456 
variation of speed, 472, 473 

Dynamo room 
care, 842 

Dynamometers 
absorption, 484 
Siemens, 675 
transmission, 484 

Dynamotors 

description, 452 
use, 452 

Dyne 

C. G. S. unit of force, 12 

Earth test, 709 

Ebonite 

table of insulators, 51 

Eccentric rod and strap 

engine, Gen. Elec. Co. Form 

H-l, 519 
engine, Gen. Elec. Co. Form 

H-2, 532 

Eddy currents, 171, 172, 195 

Edison 

alkaline secondary cell, 83 
telephone transmitter, 740 



Efficiency, efficiencies 
generators, 193, 478 

commercial, 194, 478 

electrical, 194 

gross, 193 
incandescent lamps, 586 
motors, 272 

commercial, 482 

electrical, 274 

gross, 273 

net, 275 
secondary cells, 82 
variable speed gear, 396, 397 

Elbows 90° 

conduit fittings, 655 
outlet 90°, 655 
outlet 45°, 655 

Electrical 

efficiency of generators, 194 
efficiency of motors, 274 
losses of generators, 194, 195, 

196, 197 
losses of motors, 275, 276 

Electrical Interior Communication, 
762 
cable, 764 

dimensions, 765 
tests, 767 
conductors, 763 
general means of, 768 
battle and range order cir- 
cuits, 768 
call-bell circuits, 768, 769 
fire-alarm circuits, 768 
fire-control circuits, 768 
general alarm circuits, 768 
telegraph circuits, 768 
engine, 768, 800 
helm, 768, 800 
telephone circuits, 768, 777 
warning signal circuits, 768 

Electricity 

C. G. S. unit quantity, 18 

Electric machines 
dynamo, 444 

Electric oscillations 
definition, 872 

Electric plant 
care, 832 






Index 



947 



Electrochemical action 
examples, 54 

Electrochemical effect, 674 

Electrochemical series 
table, 54 

Electrodes 

arc lights, 596 
primary cells, 55 

Electrolytes 
definition, 54 
primary cells, 53 
secondary cells, 75, 81 

Electrolytic 
detectors, 900 
interrupters, 881 

Electromagnet, 125 
disc brake, 359 
examples, 126, 127, 128 

club foot, 126 

double coil, 126 

iron clad, 127 

long range, 128 

one coil, 127 

stopped, 128 

Electromagnetic 
unit of current, 18 
unit of E. M. F., 22 
unit of resistance, 23 
waves, 883 

applied to telephones, 919 

detachment from aerials, 
891, 892 

properties, 884, 885, 886 

stationary, 896 

Electrometer 

Sir Wm. Thompson, 58 

Electrostatic effect, 674 

Elements 

definition, 55 
secondary cells, 77 

Elevating 

gun equipment, 397 
connections, 398, 400 
direct system, 397 
elementary connections, 398 
motor gearing, 399 
motor generator system, 399 



E. M. F. 

applied, of motors, 261, 262 

calculation of induced, 172, 173, 
174 

C. G. S. unit, 22, 154, 155 

comparison of cells with test- 
ing set, 707 

counter due to self-induction, 
428 

counter, in arc lights, 597 
explanation, 597 

counter, in circuit, 92 

counter of motor, 261, 262 

curve, 158, 159, 427 

curve after commutation, 167 

curve and resultant E. M. F., 
432 

curve applied, in alternating 
currents, 431 

curve before commutation, 167 

curve due to two coils, 167 

curve of and charging current, 
437 

curve of current and power, 
440 

curve of total, 170, 171 

curve showing superposition, 
168 

determination around arma- 
ture, 493 

difference of potential, 19 

effect of sp. gr. of solution, 81 

energy, 442 

expression, 155 

generation, steady and in- 
creased, 166, 167, 168, 169, 
170 

idle, 442 

illustration, 20, 21 

induced, in a closed coil, 156, 
157, 158 

induced, in a closed surface, 
158 

magnitude of resultant, 434 

measurement, 699 
with voltmeter, 699 
primary cells, 58 

practical unit, 22 

primary cells, 58 
open circuit, 58 

relation in motor generators, 
445 

relation to speed of motors, 
261 

resistance, 431 



948 



Index 



E. M. F.— Cont'd 

self-induction, 428 
variation in alternating cur- 
rents, 425, 426 

Enclosed arc lamps 
description, 609, 610 

End feeders, 632 

Energy- 
definition, 14 
kinetic, 14 
potential, 14 

Engine 

indicator circuits, 768, 801 
revolution indicator, 801 
telegraph circuits, 768, 797 
telegraph indicator, 799 

Engines 

care, 840, 841, 842 
early types, 502 
Forbes 100 K. W., 541, 542 
governor, 541 

operation, 541, 542 
piston-rod packing, 543, 544 
Gen. Elec. Form H-l, 514 
connection rod, 524 
crank shaft and coupling, 

523 
cylinders, 514 

eccentric rod and strap, 519 
governor, 519, 520 
connecting rod, 521 
instructions for removing, 
521 
grease cups, 521 
. high-pressure valve, 517 
indicator motion, 522 
low-pressure valve, 517 
lubrication, 525 
main bearings, 527 
piston rod and cross-head, 

522 
piston-rod packing, 528 
rocker arm, 519 
sectional view, 515 
starting, 527 
steam distribution, 516 
steam pressure, 514 
throttle valve, 524 
valve stems, 518 
stuffing-box, 519 



Engines — Cont'd 

Gen. Elec. Form H-2, 529 
crank shaft and coupling, 534 
cross-head, 533 
cylinders, 529 
draining arrangement, 530 
eccentric rod and strap, 532 
governor, 536 

operation, 536 
high-pressure valve, 531 
indicator motion, 538 
low-pressure valve, 532 
lubrication, 537, 538 
piston rod, 533 
pistons and packing, 532 
starting, 538 
steam pressure, 529 
' throttle valve, 535 
valve-stem stuffing-box, 530 
oil, 554 

Hornsby-Akroyd, 556 
specifications, 502, 503, 504, 

505, 506 
Sturtevant 100 K. W., 545 
tandem-compound, 507 
connecting rod, 510 
crank shaft, 511 
governor, 511 

instructions for removing, 
511 
lubrication, 512 
main bearings, 511 
pistons, 509 
rod, 509 

packing, 509 
steam valves, 507 
stems, 509 
torpedo boats, 538 

Gen. Elec. 6-5-700, 539 
governor, 2% K. W., 540 
governor, 5 K. W., 539 

Equalizer, -ing 

necessity, 213 
load, 214 

Equation 

direct-current generator, 174 
dynamo, 201 
fundamental motor, 264 
fundamental wireless tele- 
graphy, 876 

Equator 

earth's magnetic, 109 






Index 



949 



Equipment 

boat cranes, 411 
gun elevating, 397 

direct system, 397 

motor-generator system, 399 
gun loading, 399 
mechanical, chain hoists, 408, 

409 
miscellaneous, 424 

controlling panel, 424 
ventilation, 418 

water-tight door and hatch, 422 
whip hoists, 409, 411 

Erg 

C. G. S. unit of work, 13 

Evershed testing set, 695 
connections, 696 

Examples 

acceleration, 12 

calculation size of wire, 623, 
624, 625 

capacity, 30 

energy, 15 

force, 13 

insulation resistance, 718 

losses in dynamo machines, 491 

phase and voltage alternating 
current, 427 

Swinburne's test, 482 

use of voltmeters and amme- 
ters, 677, 678 

work, 15 

Factor 

power, 442 

relation to true watts, 442 

Fall of potential 
explanation, 20, 21 

Fans 

desk, 421 

connections, 421 

Farad 

definition, 873 
micro, 30, 873 
practical unit of capacity, 30 

Faults 
annunciator systems, 776 
generators and motors, 724. 

725, 726, 727, 728 
test by magneto, 711 



Faults— Cont'd 

tests for and location 

fracture in armature, 734 

fracture in field windings, 
735 

grounds in armature, 734 

grounds in external circuit, 
730 

grounds in field, 734 

short circuit in armature, 
732 

short circuit in external cir- 
cuit, 729 

short circuit in field, 733 
connections for testing, 
733 

Faure 

cells, 77 

Feeder, feeders 
bus, 630 
center, 632 
end, 632 
general, 629 
junction boxes, conduit, 648, 

650 
junction boxes, molding, 649, 

651 
interior fittings, 652 
marking, 634 
riser, 633 
sub, 630 
two-wire system, 629 

Field 
coils, insulation, 100 K. W., 

247, 248 
connections, rotary comp. sys- 
tem, 385 
fracture, 735 

frame, generator 6-32-80, 227 
generator and motor for turret- 
turning, 370 
generator for Ward-Leonard 

control, 371 
generator, 100 K. W., 244 
core, 244 
frame, 244 
poles, 244 
windings, 244 
grounds, 734 
losses in generators, 196 
magnets, service generators, 
218, 219 



950 



Index 



Field— Cont'd 

motor, for Ward-Leonard con- 
trol, 372 
regulation for speed control, 

285 
relation to speed of motors, 

267 
resistance control of motors, 

268 
short circuits, 733 
windings, 6-32-80 generator, 

231 
windings, 100 K. W. generator, 

244 
windings, service generators, 

224 

Field coils 

boat-crane motor, 305 

chain ammunition-hoist motor, 

299 
Sturtevant blower motor, 310 
turret-turning motor, 302 

Field, magnetic, 22, 109 
bar magnet, 110 
current in coiled conductor, 

121, 122 
current in straight conductor, 

115 
measurement, 133, 134 
motor, 257, 258, 259 
parallel conductors, 118, 119 
reaction of two, 117 
resolution of forces, 120 
telephone receiver, 739 
unit, 111 

Filament, incandescent lamps 
carbonizing, 580 
flashing, 581 
forming, 579 
shaping, 580 
tantalum, 593 
tungsten, 593 
types, 582 

Fingers 

adjustment, 847, 848 
contact for commutating 

switch, 386 
contact for controllers, 342 
contact for controller, rotary 

compensator system, 385 



Fire alarm 

annunciators, 775, 776 
circuits, 768, 804 

Fire-control circuits, 813 

broadside ammunition hoist, 

813, 825 
cease-firing circuits, 813, 827 
range and deflection circuits, 

813, 820 
salvo firing circuits, 813, 823 
telephone system, 813, 814 

Firing, cease 

circuits, 813, 827 
gongs, 827 

Fittings, interior 

5-ampere switch, single pole, 
653 
25-ampere switch, double pole, 

653 
50-ampere switch, double pole, 

653 
50-ampere switch, double pole, 
double throw, 653 
5-ampere receptacle, 653 
5-ampere switch and recepta- 
cle, 653 
25-ampere switch and recepta- 
cle, 653 
feeder boxes, 652 
main junction boxes, 653 

Fixtures, 657 
care, 870 
lanterns, 662 
battle, 662 

cargo reflector, 662, 663 
deck, 662 
desk, 662 

magazine, 662, 665 
portables, 662, 666 
non-water-tight, 666 
water-tight, 666 
regular, 657 

bracket, single, double, 657 
bulkhead, 657, 659 
bunker, 657, 659 
ceiling fixture, commercial, 

657, 661 
ceiling fixture No. 1, 657, 660, 

661 
ceiling fixture No. 3, 657, 661 
deck, 657, 658 
drop, 657, 658 
overhead bunker, 657, 660 



Index 



951 



Fixtures — Cont'd 
special, 666 

binnacle, 666, 667 
blinker signal, 666, 669 
diving lantern, 666, 667, 668 
masthead lantern, 666, 669 
night signal lantern, 666, 670 
peak lights, 666, 670 
range lights, 666, 670 
side lights, 666, 669 
signal lanterns, 666, 670 
stay light, 666, 671 
telegraph fixture, 666, 672 
top lantern, 666, 670 
towing lantern, 666, 670 
truck light, 666, 671 
turret hood, 666, 672 

Flaming 

arc lights, 613 

Flanges 

armature 6-32-80 generator, 228 
armature insulation 100 K. W. 
generator, 245 



incandescent lamp, 



Flashing 
filament, 
581 

Fleming wave meter 
description, 906 
tuning closed sending circuit, 

910 
tuning open sending circuit, 

911 

Flux 

magnetic, 129 

Foot-pound 
definition, 14 
relation to foot-poundal, 14 

Foot-poundal 
definition, 14 
relation to foot-pound, 14 



Forbes 

engine 100 K. 
541, 542 

Force 

C. G. S. unit, 12 
coercive, 133 



W. generator, 



Force— Cont'd 

earth's magnetic, 108 

horizontal, 109 

total, 108 

vertical, 109 
examples, 13 
laws, magnetic, 111 
lines, 112 

lines due to magnetic pole, 111 
magnetizing, due to solenoid, 

124 
magnetomotive, 130 

Form H-i engine 
Gen. Elec. Co., 514 

Form H-2 engine 
Gen. Elec. Co., 529 

Forming 
filament, incandescent lamps, 

579 
secondary cells, 77 

Formula 

brake horsepower, 483 

Four-way junction boxes 
conduit wiring, 648, 650 
interior fittings, 653 
molding wiring, 651 

Fracture 

armature, 734 
field winding, 735 

Frame 

boat-crane motor, 303 

chain ammunition-hoist motor, 

298 
commutating switch, 386 
controller, 340 
controller, rotary compensator, 

386 
disc brake, 359 
field, generator, 6-32-80, 227 
field, generator, 100 K. W„ 244 
magnet, rotary compensator, 

449 
Sturtevant blower motor, 309 
turret-turning motor, CB-24, 

301 

Frequency 

definition, 427, 872 

expression, 428 

relation to wave length, 885 



952 



Index 



Friction 

losses, 486, 488 

curve, 489 

determination, 486, 488 

example, 491 

instructions for curve, 486 
losses in generators, 195 

Fuses, 639, 640 

calculation for size, 640, 641 
care, 845 

replacing, 845 
location, 644, 645 
multiple, 642 
requirements, 640 
shapes, 643 

speed-controlling panel, 333 
standard controlling panel, U. 
S., 330 

Galvanic batteries (see Batteries, 
primary) 

Galvanometers, 685 

service testing set, 689 
testing set, 689 

Gas 

resistance, 57 

Gaskets, 656 

method of designating, 657 
type A, 656 

Gauss 
C. G. S. unit magnetic field, 17 

GE-800-E 
type of motors, 303 

Gear 
variable speed (see Variable 
speed gear) 

Gearing 

elevating system, 319 
turret-turning system, 368 

General alarm 
circuits, 768, 806 
contact maker, 806 
wiring, 807 

Gen. Elec. Co. engines 
torpedo boats, 538 

governor 5 K. W. set, 539 
operation, 540 



Gen. Elec. Co. engines — Cont'd 
governor 2% K. W. set, 540 
operation, 541 

Gen. Elec. Form H-i engine, 514 

Gen. Elec. Form H-2 engine, 529 

Generating sets 

care, after stopping, 832 

Generator, motor (see Motor gen- 
erators) 

Generators 
as motors, 270, 271 
building up, 189 
commercial efficiency, 478 
direct method, 478 
indirect method, 479 
compound, 188,. 189 
as motor, 272 

long shunt, dynamo equa- 
tions, 205 
short shunt, dynamo equa- 
tions, 204 
efficiencies, 193, 478 
elementary theory, 154, 155 
engines, specifications, 502, 503, 

504, 505, 506 
faults, table, 724, 725, 726, 727, 

728 
field control for turret turning, 

366 
field for generator and motor 

control, 370, 371 
fundamental equation, direct 

current, 174 
losses, 194, 195, 196, 197 
motive power, 499 
overrunning, 585 
problems, 205, 206, 207, 208, 

209 
running in parallel, 210 
separately excited, 176, 177 
series, 176, 177, 178 
as motor, 270, 271 
dynamo equations, 202 
regulation, 179 
shunt, 183, 184 
as motor, 271 
dynamo equations, 203 
regulation, 185 
underrunning, 585 
uses of different classes, 192 



Index 



953 



Generators, types 
Form D 8-32-80, 235 

headboard, 237 
100 K. W., 242 
armature, 242 
commutator, 243 
core, 243 
spider, 242 
windings, 244 
300 K. W. turbine-driven 
specifications, 252, 253, 254, 
255 
M. P. 6-16-125, 237 

specifications, 237, 238, 239, 
240 
M. P. 6-32-80, 227 
armature, 228, 229 
insulation, 230 
slots, 230, 231 
binding wires, 231 
brushes and holders, 233 
brush rocker, 234 
commutator, 231 
conductors, 231 
connectors to commutator, 

231 
field frame, 227 
field windings, 231 
series shunt, 233 
series winding, 233 
shunt winding, 233 
spool insulation, 232 
service, 217 

armatures, 220, 221 
commutator, 223 
conductors, 222 
core, 220 

cross-connections, 222 
brushes, 224 

material, 225 
field windings, 224 
forms of field magnets, 218, 

219 
general characteristics, 217 
general requirements, 218 
headboards, 226, 227 

German silver 
constituents, 35 
resistance, 38 
specific, 37 
table of conductors, 34 
use, 35 

Glass 

specific resistance, 37 



Glass— Cont'd 

table of insulators, 51 
use, 52 

Gold 

annealed, resistance, 38 
diamagnetic, 114 
electrochemical series, 54 
melting point, 39 
resistance, hard drawn, 38 

Gongs 

cease-firing, 827 
general alarm, 806 
care, 808 

Governors 

Forbes engine, 100 K. W., 541 

operation, 543 
Gen. Elec. Engine Form H-l, 
519 
instructions for removing, 
521 
Gen. Elec. Engine Form H-2, 
536 
operation, 536 
Rites, 5 K. W. Gen. Elec. En- 
gine, 539 
operation, 540 
Rites, 2V 2 K. W. Gen. Elec. En- 
gine, 540 
operation, 541 
tandem-compound engine, 511 
instructions for removing, 
511, 512 

Grease cups 
care, 860 

compression, care, 859 
Gen. Elec. Engine Form H-l, 
521 

Gross 

efficiency of generators, 193 
efficiency of motors, 273 

Ground detectors 
lamp, 571, 730 

connections, 730 
standard switchboard, 571 
voltmeter, 571, 731 

connections, 731 

Grounds 

armature, 734 
external circuit, 730 
field, 734 
tests by magneto, 711 



954 



Index 



Grouping of Cells 
multiple, 64 
multiple series, 65 
series, 63 

Gunboat 

distribution of current, 637 

Gunboat class 

switchboards, 560, 561 
search-light panel, 562 

Gun-elevating equipment 

connections, turret guns, 398 
diagram of connections, 398 
direct system, 397 
motor-generator system, 399 
specifications for motor gener- 
ator, 446, 447, 448 

Gutta-percha 
specific resistance, 37 

Hammer 
interrupter, induction trans- 
former, 877, 880 

Handle 

controller, 344 

Hatches 

water-tight equipment, 422 

Headboards 
generator, Form D 8-32-80, 237 
generator, service, 226, 227 

Heat 

British unit, 16 

calorie, 16 

C. G. S. unit, 16 

electrical unit, 26 

examples, 29 

generation, 38 

limit output of generators, 198 

relation to resistance, 38 

remarks, 736 

test, 736 

Heating 

general, dynamo machines, 474 
change of resistance, 475 
method of calculation, 475 
temperature, rise, 474 
thermometer, rise of, 474 

Heating effect, 674 



Helm 

telegraph, 799 
wiring, 800 

Henry, 874 

practical unit of inductance, 31 

High frequency alternating cur- 
rents 
definition, 872 

Hoists, ammunition 
chain, 408 

connections, 408 

equipment, 408 
chain, motor, 298 
turret, 405 

diagram of connections, 408 

Hoists, whip 

diagram of connections, 411 
electrical connections, 410 
electrical equipment, 411 

Holder, holders 
brush, generator, M. P. 6-32-80, 

233 
brush, service generators, 225, 
226 

Holtzer- Cabot Electric Co. 
gun-head telephone set, 787 
intercommunicating telephone 
system, 757 

Hornsby-Akroyd 
oil engine, 556 

Horsepower 

' convert to" B. T. U. per sec, 28 
convert to calories per sec, 28 
convert to ergs per sec, 26 
convert to ft.-lbs. per min., 26 
convert to ft.-lbs. per sec, 26 
convert to kilowatts, 26 
convert to watts, 26 
definition,' 25 
lines, 182, 183 
relation to watts, 25 

Hot wire 

ammeter, 908 

Hughes 

microphone, 740 

Hunning 
telephone transmitter, 740 



Index 



955 



Hydrogen 

electrochemical series, 54 

Hysteresis 

loss in generators, 195, 196, 487 

Illumination 
candle-foot, 591 
general remarks, 591, 592 

Impedance, 874 

alternating currents, 435 

triangle of resistance, 435 
due to capacity, 438 
due to capacity and induction, 
439 

Incandescent lamps (see Lamps) 

Indicator, indicators 
circuits, 768 
battle order, 810 
engine, 768 

engine revolution, 801 
engine telegraph, 799 

wiring, 799 
helm, 768 
helm angle, 802 
helm telegraph, 799, 802 

Indicator cards 
Otto cycle, 555 

Indicator motion 

engine, Gen. Elec. Form H-l, 

522 
engine, Gen. Elec. Form H-2, 
538 

Inductance 

C. G. S. unit, 31 

electrical vibration, 878 

examples, 31 

forms, 883 

henry, 31, 874 

practical unit, 31 

receiving circuits, wireless 

telegraphy, 901 
variable, 883, 902 

Induction 

coils, 150, 151 

coils for creating electric oscil- 
lations, 152 
coils for telephones, 745 

connection, 746 
electromagnetic, 136, 142 



Induction — Cont'd 

illustration, 139, 140, 141 
laws, 138 
lines, 112, 113 
magnetic, 113 
methods, 142 

electromagnetic, 142 

mutual, 143, 146 

self, 142, 143, 144 
mutual, coefficient, 149 
principles, 137, 142 
self, coefficient, 145, 146 

Inductive 

forms of circuit, 144 

Influence 

magnetic, 113 

Input 

generators, 194 

Inspections 

circuit breakers, 863 
controllers, 862 
motors, 862 
rheostats, 863 

Installation 

conduit wiring, 636 
molding wiring, 636 

Instruments, 673 
calibration, 702 
electrochemical effect, 674 
electrostatic effect, 674 
heating effect, 674 
magnetic effects, 674 

Instrument boards, 560 

Insulation 

armature, 100 K. W. generator, 

.245 
armature, M. P. generator 
6-32-80, 230 
conductors, 231 
slots, 230, 231 
conductors, service generator, 

223 
definition, 50 
double conductors, 619 
diving lamp, 620 
plain, 619 
silk, 619 
field coils, 100 K. W. generator, 
247 



956 



Index 



Insulation — Cont'd 

series coils, 247, 248 
shunt coils, 248 
field windings, service genera- 
tor, 224 
lighting wire, 617 
resistance 
dynamo electric machines, 

473 
measurement, 712 
direct deflection, 713 
example, 718 
machines, 714, 715 
ohmmeter, 719 
testing set, 713 
voltmeter, 716, 717 
single conductor, 618 
spool, M. P. generator, 6-32-80, 

232 
tests of conductors, 620 
twin conductors, 618 

Insulators 
definition, 34 
properties, 50 
table, 51 
use, 51 

Intensity 

magnetization, 112 

Intercommunicating system, Ness 
interior telephones, 757 

central talking and ringing, 

760 
local talking, central ring- 
ing, 757, 758 
local talking, magneto ring- 
ing, 757, 759 

Interior communication, 762 
switchboard, 831 

International units 
capacity, 33 
current, 32 

electromotive force, 32 
induction, 33 
power, 33 
quantity, 32 
resistance, 31 •' 
work, 33 

Interrupters 

forms, induction transformers, 
880 



Iron 

annealed, resistance, 38 
cast, melting point, 39 
electrochemical series, 54 
losses, determination, 486 

construction of curve, 487 

example, 491 

instructions for curve, 486 
paramagnetic, 114 
specific resistance, 37 
table of conductors, 34 
wrought, melting point, 39 

Jacks, spring 

telephone switchboard, 752 

Jet 

interrupter, induction trans- 
former, 880 

Joints 

resistance, 49 

Joubert 

determination E. M. F. around 
armature, 495, 496 

Joule 

definition, 26 
relation to calorie, 27 

Junction boxes 

conduit wiring, 648, 650 

feeder, 648, 650 

four (4) way, 648, 650 

main, 648, 650 

three (3) way, 648 
interior fittings, 652, 653 
molding wiring, 651 

feeder, 65 

four (4) way, 651 

main, 651 

three (3) way, 651 

Kathode 

primary cell, 55 
secondary cell, 75 

Keys 

calling, telephone switchboard, 
755 

listening, De Forest wireless 
telephone, 926 

listening, telephone switch- 
board, 755 

service testing set, 691 

testing set, use of, 709 



Index 



957 



Kirchoff's laws, 95 

illustration, 103, 104, 105, 106 

Kilogramme 
unit of mass, 9 

Kilowatt 

definition, 26 

Kine 

C. G. S. unit of velocity, 10 

Lag 

angle, 432 

Laminations 

armature cores, 172 

Lamp 

ground detector, standard 
switchboard, 571 

index, De Forest wireless tele- 
phone, 926 

line, telephone switchboard, 
754 

supervisory, telephone switch- 
board, 755 

Lamps, arc 

enclosed, 609, 610 

horizontal, description, 602, 

603, 604 
requirements, 599 

Lamps, incandescent 
candle-power, 584 
comparison, 584 
efficiency, 586 
general explanation, 578 
life test, 590 
manufacture, 579 
bulb, 582 

exhausting, 582 
filament, 579 
carbonizing, 580 
flashing, 581 
forming, 580 
shaping, 580 
stages of assembly, 582 
Nernst, 593 
standard, 584 
standard forms, 587 
table of characteristics, 588 
table of tests, 589 
tantalum, 593 
tungsten, 593 



Lanterns 
battle, 662 
deck, 662 
diving, 662 
magazine, 662, 665 
masthead, 669 
night signal, 670 
signal, 670 
top, 670 
towing, 670 

Law 

maximum activity, motors, 
273, 274 

Laws 

divided circuits, 95 

illustration, 103, 104, 105, 
106 
induction, 138 
Kirchoff, 95 
Lenz, 139 

magnetic circuit, 130 
magnetic force, 111 
parallel currents, 118 
resistance, 36 

Lead 

angle, 433 

Lead 

diamagnetic, 114 
electrochemical series, 54 
melting point, 39 
resistance, pressed, 38 
specific resistance, 37 
table of conductors, 34 
use of alloys, 35 

Lead oxide, 79 

Lead peroxide, 75 

Lead sulphate, 78 

Leakage 

electricity, 50 
secondary cells, 86 

Leaks 

magneto test, 711 

Leclanche battery 
chemical action, 71 

Legal units (see International 
units) 

Length 
unit, 9 



958 



Index 



Lenz's law, 139 

Leonard 

system motor control, 281, 282 

Life 

incandescent lamps, 585, 590 

Light 

comparison, 584 

Lights, arc 

general principles, 595 

Lighting circuits 

battle service, 628 

lighting service, 628 

plan, 629 

two-wire system, 629 
three-wire system, 645, 646 

size of wires, 621 

Lighting service, 629 

Lines 

force, 112 

due to magnet pole, 111 
horsepower, 182, 183 
induction, 112 

Litharge, 78 

Load 

equalizing of generators, 214 
equalizing of turret motors, 
851 

Loading 

gun, equipment, 399 
controller, 402 
electrical connections, 401 
elementary diagram, 402 
safety clutch, 403 

Local action 

primary cells, 57 
secondary cells, 86 

Local hattery system 

telephone connection, 747 
bridging connections, 748 
series connections, 747 

Loop 

parallel, system of wiring, 633 
system, 630, 631 

Losses 

armature, generators, 196 
construction of curve, 487 



Losses — Cont'd 

core, generators, 196 
curves of no load, 489 
curves of separation, 487 
example, 491 
field, generators, 196 
general remarks, 486 
generators, 194, 195 
iron and friction, 486 
instructions for obtaining, 
486 
motors, 275, 276 

Lost 

amperes, 183 
volts, 181 

Lubricants 
care, 858, 861 

Lubrication 
boat-crane gear, 856 
chain ammunition hoists, 855 
engine, Gen. Elec. Form H-l, 

525, 526 
engine, Gen. Elec. Form H-2, 

537, 538 
engine, tandem-compound, 512, 

513 
turret-turning system, 851 
ventilation sets, 857 

Machines 

dynamo electric, 444 
general tests, 456 

Magazine lantern, 662 

Magnet, magnets, 107 
bar, field, 110 

blow out for controllers, 343 
field, forms of generators, 218 
no-load release, 333 
no-voltage release, 326 
overload, 327 

overload for speed control 
panel, 333 

Magnetic 

blow-out for circuit breakers, 
349 

circuit, 129, 131 

circuits, closed, 125 

circuits, double in electromag- 
nets, 128 

circuits, laws, 130 

circuits, open, 125 



Index 



959 



Magnetic — Cont'd 
detectors, 896, 899 
effect, 674 
equator, 109 
field, 22, 109 

definition, 22 

due to bar magnet, 110 

due to current in coiled con- 
ductor, 121, 122 

due to current in straight 
conductor, 115 

measurement, 133, 134 

reaction of two, 117 

unit, 17, 111 
flux, 129 
force 

earth's, 108 

laws, 111 
induction, 113 
moment, 112 
permeability, 115 
pole, unit, 16, 111 
poles of earth, 107 
potential, 129 
susceptibility, 115 
typical circuit, 131, 132 

Magnetism 
definition, 107 
electro, 115 
free, 110 
residual, 133 
test, 735 

Magnetite, 107 

Magnetization 
curves, 465 

connections, 466 

instructions, 466 
intensity, 112 

Magnetizing force 
magnetomotive force, 130 
solenoid, 124 

Magneto, 692, 693 

Evershed testing set, 697 

switchboard, 752 

uses, 710 

detecting grounds, 711 
locating faults, 711 
measuring resistance, 712 
testing for breaks or leaks, 

711 
testing for open circuit, 710 

wrong indications, 712 



Magnetomotive force 
magnetic circuit, 130 

Main junction boxes 

conduit wiring, 648 650 
interior fittings, 652, 653 
molding wiring, 648, 650 

Mains, electric lighting 
general, 629 
marking, 634 

Manganese 

electrochemical series, 54 

Manganin 

table of conductors, 34 
use, 35 

Mass 
C. G. S. unit, 10 
unit, 9 

Masthead lantern, 669 

Measuring and testing, 673 
current, 698 
resistance and voltmeter, 698 
without opening circuit, 698 
E. M. F., 699 
magnetic fields, 133, 134 
resistance 
ammeter and voltmeter, 700 
armature, 722 
battery, testing set, 708 
contact, 723 
insulation, 712 
machine, 714, 715 
ohmmeter, 719 
voltmeter, 716, 717 
example, 718 
series winding, 721 

connections, 721 
shunt windings, 720 
bridge, 720 

voltmeter and ammeter, 
720 
voltmeter, 700 

connections, 700 

with voltmeter, 699 

connections, 699 

Mechanical 

losses in generators, 194, 195 
strength, electric machines, 

458 
units, derived, C. G. S. system, 

10 



960 



Index 



Megohm, 24 

Melting points 
table, 39 

Mercury- 
definition of ohm, 31 
diamagnetic, 114 
electrochemical series, 54 
specific resistance, 37 
table of conductors, 34 

Mercury vapor 
arc lights, 613 

Meters, wave, 903 
Donitz, 904, 905 
Fleming, 906, 907 
Pierce, 908 
Slaby helix, 904 

Metre 

unit of length, 9 

Metric system 
standards, 9 

Mho 

unit of conductivity, 46 

Mica 
table of insulators, 51 
use, 51 

Microfarad 
definition, 30 

Microhm, 24 

Microphone 

De Forest wireless telephone, 

927 
Hughes, 740 

Mil 

circular, 614 

relation to square inch, 614 
relation to square mil, 614 

square, 614 

Milliampere 

unit of current, 18 

Millivolt, 22 

M. L. 

circuit breakers, 352 

Moisture 

general effects, 843 



Molding, 656 
backing strip, 656 
capping, 656 
wiring appliances, 651 
wiring installation, 636 

Moment 

magnetic, 112 

Mordey 

determination E. M. F. around 

armature, 495 

Motive power 
generators, 499 

Motor, motors 

ammunition hoist, 308 
automatic control, 339 
boat crane, revolving, GE-800- 

E, 303 
CB-15, 293 

exploded view, 294 
CB-24, 301 
CB-25, 295, 305 

exploded view, 296 

longitudinal section, 297 
CB-27, Form B, 300 

assembly, 301 
CB-32, 303 

exploded view, 304 
CB-34, exploded view, 306 
chain ammunition hoist, 298 
commercial efficiency, 482 
compound, 269 

as generator, 272 
control, 277 

Day, 283, 284 

Leonard, 281, 282 

Panel, 285 
controlling devices, 324 
counter E. M. F., 261, 262 
CR, Form G, 307 
efficiencies, 272 
electrical construction, 298 
faults, table, 724, 725, 726, 727, 

728 
field for generator and motor 

control, 372 
fundamental equation, 264 
gearing for gun elevating, 399 
gearing for turrets, 368 
GE-800-E, 303 
losses, 275, 276 
operation, 277 
problems, 286, 287, 288, 289 



Index 



961 



Motor, motors — Cont'd 
series, 268 

control, 278 

regulation, 269 
service, 290 
shunt, 265 

connections, 265 

control, 279 
specifications, 291, 292, 293 
starting devices, 324 
Sturtevant blower, 308, 309 
theory of control, 256 

general principles, 256 
torque, expression, 260, 261 
turret-turning CB-24-35H-80V, 

301 
types, 293 
used as generators, 270, 271 

Motor circuits 
installation, 629 
size of wire, 622 

Motor generators 

connections for turret turning, 

376 
relation of E. M. F.'s, 445 
specifications, 373, 374, 375, 376 
specifications for gun elevat- 
ing, 446, 447, 448 
system for elevating, 399 

connections, 400 
system of turret control, 373 

Motor turbine 

interrupter, induction trans- 
former, 880 

M. Q. 

circuit breakers, 350 

Multiple 

grouping of cells, 64 

resistance, 46, 47 

series grouping of cells, 65 

Multiplier 

shunt currents, 98 

Mutual 

induction, coefficient, 149 

Needle 

compass, 107 

Evershed testing set, 697 

Nernst lamp, 593 



Ness 

intercommunicating telephone 
system, 757 

Net 

efficiency of motors, 275 

Never 

instructions for operation, 864 

Nickel 

constituent German silver, 38 
electrochemical series, 54 
paramagnetic, 114 

Night signal lantern, 670 

Night signal set 
cable, 764, 767 
care, 867 

Nipples 

conduit fittings, 655 

Noise 

running dynamo machines, 460 

No voltage 

release magnet, 326, 333 

Office calls, 769 

Ohm 

megohm, 24 
microhm, 24 
practical unit of resistance, 24 

Ohm's law, 23, 88, 90 
application to simple circuits, 

90, 91 
problems, 88, 89 

Ohmmeter, 694 
coils, 695 
insulation resistance, 719 

Oils 

table of insulators, 51 
use, 52 

Oil engines (see Engines) 

Okonite 

use, 52 

Operating 

in parallel, instructions, 214, 
215 



962 



Index 



Operation 

automatic brake boat cranes, 
414 
hoisting, 414 
lowering, 415 
controllers, 849, 850 
De Forest wireless telephone, 

922 
description panel, U. S., 330 
description speed-control pan- 
el, 331 
directions panel, U. S., 331 
directions speed-control panel, 

334 
instructions, 863 
always, 863 
never, 864 
motors, 277 

order, turret-turning system, 
851 
cautions, 853 
starting 

dynamo room, 851 
turret, 851 
stopping 

dynamo room, 852 
turret, 852 
order, ventilating sets, 857 
starting, 857 
stopping, 858 
Ward-Leonard system, 363 

Oscillations, electric, 875 
damped, 872 

feebly, 873 

strongly, 873 
definition, 872 
high frequency, 875, 876 
induction coil for creating, 152 
intermittent damped, 872 

production, 872 
sustained, 872 
transformer, 879 

Otto cycle, 554 

explanation, 554, 555 

admission, 554 

compression, 554 

exhaust, 555 

ignition, 555 
indicator card, 555 

Output 

Brackett's cradle, 485 
generators, 194 

limit, 198 
secondary cells, 81 



Overload release magnet 

motor-control panel, 327, 333 

Overrunning 

generators, effect, 585 

Oxygen 

electrochemical series, 54 

P 

controllers, 348 

Packing 

piston, Gen. Elec. Form H-l 

engine, 523 
piston, Gen. Elec. Form H-2 

engine, 532, 533 
piston rod, Katzenstein, Forbes 

engine, 543, 544 
piston rod, tandem-compound 

engine, 510 

Panel, panels 
chain ammunition-hoist motor, 

300 
circuit switch fire-control tele- 
phones, 827 
control of motors, 285 
controlling, chain ammunition 

hoists, 407 
controlling, miscellaneous 

equipments, 424 
controlling, navy standard 
type, U. S., 327, 328, 329 
circuit breaker, 330 
construction, 327 
description of operation, 330 
direction for operating, 330 
fuses, 330 
insulation, 330 
resistances, 330 
rheostat switch, 328 
switch, 328 
terminals, 330 
controlling, ventilating sets, 

421 

search-light, gunboat class, 562 

speed controlling 

description of operation, 334 

directions for operating, 334 

field-regulating rheostat 

switch, 333 
fuses, 333 
insulation, 333 
no-load release magnet, 333 
overload release magnet, 333 



Index 



963 



Panel, panels — Cont'd 
resistances, 333 
rheostat switch, 333 
switch, 333 
terminals, 333 
starting, elevating equipment, 

399 
starting, rotary compensator, 

383 
switch, elevating equipment, 

397 
type CR, Form M-3, 336, 337 
water-tight, flame-proof, 339 



Phase 

definition, 427 

Phosphor bronze 

table of conductors, 84 
use, 35 

Pierce wave meter 
description, 908 

tuning, closed sending circuit, 
910 
open sending circuit, 

911 
receiving circuit, 913 



Paper 

table of partial conductors, 34 


Pistons 




use, 52 


engine, Gen. Elec. Form 
522 


H-I 


Paraffin 


cross-head, 522 




table of insulators 


packing, 523 




use, 52 


rod, 522 

rod packing, 528 




Parallel 


engine, Gen. Elec. Form 


H-2, 


charging of secondary batter- 


532 




ies, 84 


packing, 532 




connecting compound ma- 


rod, 533 




chines, 213 


Forbes engine, 544 




connecting series machines, 


rod packing, 544 




213 


Katzenstein, 543 




connecting shunt machines, 


tandem-compound engine, 


509 


213 


rod, 509 




generators, 210 


rod packing, 510 




operating, 214, 215 






resistances, 47, 48 


Plante 




Parallel connections 


cells, 76 




standard switchboard, 571 


Platinoid 




Parallel wiring system, 631, 632 


specific resistance, 37 




loop, 633 


Plate 




three-wire system, 645 


cap, controllers, 344 




two-wire system, 629 


end, variable speed gear, 


394, 


Paramagnetic substances 


396 
mid, variable speed gear, 


394, 


definition, 114 


396 




Partial conductors 


Plates 




table, 34 


definition, 55 




Peak lights, 670 


Platinum 




Period 


electrochemical series, 54 




definition, 426, 872 


melting point, 39 
resistance, annealed, 38 




Permeability 


specific resistance, 37 




magnetic, 115 


table of conductors, 34 




coefficient, 115 


use, 35 





964 



Index 



Platinum silver 
resistance, 38 
table of conductors, 34 

Plugs 

conduit fittings, 655 
testing set, 706 

Polarity 

rules for, 122, 123 

Polarization 

primary cells, 57 

Pole, poles 

boat-crane motor, GE-800-E, 

305 
cell, primary, 55 
effect of increase on E. M. F., 

428 
field 100 K. W. generator, 244 
magnetic, earth, 107 
north, north-seeking, 107 
pieces, chain ammunition-hoist 
motor, 298 
rotary compensator, 

450 
turret-turning motor, 
CB-24, 302 
south, south-seeking, 107 
Sturtevant blower motor, 309 
unit magnetic, 16, 111 

Porcelain 

table of insulators, 51 
use, 51 N 

Portables 

non-water-tight, 666 
water-tight, 666 

Potential 

difference, 20, 21 
fall, 20, 21 

around armature, 497 
magnetic, 129 

Poundal 

definition, 13 
foot, 14 

Powder division 

cable, 764, 766 
circuit, 812 
wiring, 812 

Power 

alternating current, 439 



Power— Cont'd 

average, 441 

C. G. S. unit, 15 

curve with E. M. F. and cur- 
rent, 440 

examples, 16, 29 

factor, 442 

practical unit, 16, 24 

source, De Forest wireless tele- 
phone, 926 

Pressboard 
use, 52 

Primary 

cell, 56 

spiral, De Forest wireless tele- 
phone, 927 

Principles 

alternating currents, 426 
operation, Leonard system, 363 
rotary comp. system, 377, 380, 

381, 382 
wireless telegraphy, 872 
telephony, 915 

Problems 

counter E. M. F., 92, 93 
divided circuits, 99, 100, 101, 

102 
generators, 205, 206, 207, 208, 

209 
grouping of cells, 69 
heat and resistance, 42 
motors, 286, 287, 288, 289 
Ohm's law, 88, 89 
resistance, 42 
shunts and comp. resistances, 

98, 99 
simple circuits, 91, 92 
wire size and drop, 627 

Projectors 

search-lights, 608 

Push buttons, 830 

Quantity 

C. G. S. unit, 18 
practical unit, 18 
relation to potential and ca- 
pacity, 436 

Quarters 

calls, 769 



Index 



965 



controllers, 346 

R-62 

controller for boat cranes, 413 

Range and deflection circuits, 820 
wiring diagram, 821 

Range indicator 
cable, 764, 766 
circuits, 768 

Range lights, 670 

Range order 
circuit, 810 

transmitter and indicator, 

810 
wiring, 813 

Reactance, 874 

alternating current, 435 

Receiver 
battle and range order, 811 
wireless telephone, 919, 928 

Audion voltage, 928 

battery B, 928 

tuning, 929 

Receivers, telephones, 743 
Bell, 744 
bipolar, 744 
Cory, 779, 780 

Holtzer-Cabot head set, 787 
navy type, early, 777 
watch-case, 745 

Receptacles 

conduit wiring, 648, 650 

5-ampere, 650 

5-ampere with hood, 648 
non-water-tight, 654 

key, 649, 654 

keyless, 649, 654 

porcelain base, 649 

Red lead, 78 

Regulation 

search-light arcs, 599 
secondary cells, 83 
series generators, 179 
shunt generators, 185 

Relay 

telephone switchboards 
cut-out, 754 



Relay— Cont'd 

line, 754 
supervisory, 755 

Reluctance 
definition, 130 

Remanence, 133 

Remedies 

generators and motors, 724, 
725, 726, 727, 728 

secondary cells, 86 

Representation 

alternating currents, 433 

Resin 

table of insulators, 51 

Resistance 

armature by comparison of de- 
flections, 461 
instructions for test, 462 

armature control of motors, 
267 

changes due to heat, 475, 476, 
477 

compensating, 97, 98 
problems, 98, 99 

contacts, imperfect, 49 

curve with time, 463 

electromagnetic unit, 23 

field, control of motors, 268, 
285 

field windings, series, 463 

joints, 49 

laws, 36 

navy standard control panel, 
type U. S., 330 

parallel, 44, 47, 93 

practical unit, 24 

primary cells, 60, 61 

problems, 42 

problems on heat, 43 

relation to heat, 38 

series, 44, 47 

series and parallel circuits, 47 

shunt windings, 463 

specific, 36 

speed-control panel, 333 

standard, 702 

table, 38 

temperature coefficient, 40 

variation with temperature, 39 

windings, in tests, 460 

working battery, 61, 62 



966 



Index 



Resistance, arc lights 
arc, 597 

apparent, 597 
ohmic, 597 
calculation dead resistance, 

601 
dead resistance, 600, 601 

Resistance coils 

service testing set, 690 
testing set, 688 
winding, 688 

Resistance, insulation 

dynamo machines, 473, 714, 715 
measurement, 712 
direct deflection, 713 
ohmmeter, 719 
testing set, 713 
voltmeter, 716, 717 
example, 718 

Resistance, measurement 

ammeter and voltmeter, 700 

precautions, 700 
armature, 722 
battery, by testing set, 708 
contact, 723 
magneto, 711 
series windings, 721 

connections, 721 
shunt windings, 720 

bridge, 720 

voltmeter and ammeter, 720 
testing set, 705 

example, 706 
voltmeter and standard resist- 
ance, 701 
voltmeter, of, 700 
voltmeter, with, 699 

Retentivity, 133 

Reversal 

currents, due to induction, 149 
magnetism, 133 
secondary cells, 77 

Rheostatic 

control of motors, 279 
series, 279 
shunt, 280 

Rheostats 

automatic, principles, 325 

care, 846 

controlling panels, 324 



Rheostats — Cont'd 

field clutch, rotary compensa- 
tor, 383 
inspection, 863 
liquid, 324 

requirements, 314, 315 
speed control, 336, 337 
switch for control panel, 328 
switch for speed control, 333 
types 

C. G., 320 

enclosed card, 318 

E. S., 322 

Form P, 324 

I. G., 321 

packed ribbon, 315 

pressed card, 317 

Rings 

annular disc brake, 359 
equalizing, 100 K. W. genera- 
tor, 251, 252 

Riser feeder, 633 

Rites 

governor, 539 

Rocker 

brush, generator 6-32-80, 234 

Rotary compensator 
description, 449 

Rotary converters 
description, 452, 453 
diagram, 452 
phase currents, 454 
relation of voltages, 454 
wireless sets, 454, 455 

Rotary transformer, 831 

Rubber 
table of insulators, 51 
uses, 51 

Rules 

current direction, 117 
hand, 118 
polarity, 122 

Sal ammoniac 

solution, 72 

Salvo firing 

wiring circuit, 823, 824 



Index 



96' 



Screw- 
control, variable speed gear, 
394 

Search-light 

arcs, regulation, 599 
care, 865 

placing carbons, 865 

placing lamp, 865 
circuits 

size of wire, 621 

wiring installation, 628 
extinguishing, 866 
focusing, 866 
operating, 866 
panel, gunboat class, 562 
projectors, 608 

Second 

C. G. S. unit of time, 10 

Secondary- 
batteries, 75 

types, 82 
spiral, De Forest wireless tele- 
phone, 927 

Section 

secondary cells, 77 

Segments 

commutating switch, rotary 
comp. system, 385 

controller, rotary comp. sys- 
tem, 386 

Selenium 

crystalline, 916 

Self-induction, 874 

alternating currents, 428 
coefficient, 145, 430 
curves of current, 429 
effect, 428 
E. M. F., 430, 431 

Senders 
wireless telegraphy, 878, 879 

Sending circuits 

wireless telegraphy 

closed, Donitz wave meter, 
909 
Fleming wave meter, 

910 
Pierce wave meter, 

910 
Slaby wave meter, 
910 



Separately excited 
generator, 176, 177 

comparison of terminal volt- 
age, 190 

Series 

charging, secondary batteries, 

84 
coils, insulation, 100 K. W. gen- 
erator, 247 
connecting machines in paral- 
lel, 213 
generator, 176, 177, 178 

characteristic curve, 180, 181 
comparison of terminal volt- 
age, 190 
dynamo equations, 202 
regulation, 179 
grouping of cells, 63 
motors, 268 

control, 278, 279 
reversing, 279 
starting, 279 
stopping, 279 
generators, 270, 271 
resistance, 47 
shunt, 6-32-80 generator, 233 

rotary compensator, 450 
winding, 6-32-80 generator, 232 
winding, measurement resist- 
ance, 721 
connections, 721 

Series connections 
telephone, 747 

Series generator, 176, 177, 178 
characteristic curves. 464 
connections, external circuit, 

464 
instructions, 464 
total circuit, 465 

Service 

generators, 217 
motors, 290 
testing set, 689 
use, 692 

Set, testing, 685 

earth test, 709 

keys, 709 
use, 709 

plugs, 706 

uses, 704 

checking ammeter, 709 
checking voltmeter, 708 



968 



Index 



Set, testing— Cont'd 

comparing E. M. F. of cells, 

707 
measuring resistance, 705 

example, 706 
measuring battery resist- 
ance, 708 
very low resist- 
ance, 706 

Shaft 

commutating switch, rotary 
comp. system, 386 

controller, rotary comp. sys- 
tem, 384 

variable speed gear, 391 

Shapes 

fuses, 643 

incandescent lamps, 587 

Shaping 

filaments, incandescent lamps, 
580 

Shellac 

table of insulators, 51 
use, 52 

Short circuit 
armature, 732 
external circuit, 730 
field, 733 

Shunt 

ampere 

connections, 684 
explanation, 683 
coils, insulation 100 K. W. gen- 
erator, 248 
connecting machines in paral- 
lel, 211, 212 
current 

multiplier, 98 
generator, 183, 184 

characteristic curves, 185, 

186, 466 
comparison of terminal volt- 
age, 191 
dynamo equations, 204 
regulation, 185 
motors, 265 
control, 279 
reversing, 280 
starting, 280 
stopping, 280 
generators, 271, 272 



Shunt— Cont'd 

series, 6-32-80 generator, 232 

rotary compensator, 450 
winding, 6-32-80 generator, 232 

Shunts 
problems, 98, 99 

Shunt generator, 183, 184 
characteristic curves, 466 
connections for external, 467 
connections for internal, 466 
instructions for external, 467 
instructions for internal, 468 

Shunt windings 

resistance, measurement, 720 
bridge, 720 
voltmeter and ammeter, 720 

Side lights, 670 

Siemen's dynamometer, 675 

Signal lantern, 670 

Silks 
table of insulators, 51 

Silver 

diamagnctic, 114 
electrochemical series," 54 
melting point, 39 
resistance, annealed, 38 

hard drawn, 38 

specific, 37 
table of conductors, 34 

Silver chloride cell 

testing set, 689 

Sines 

curve, 159 

properties, 160, 161 

Single conductors 
insulation, 618 

Size 

fuse, calculation, 640, 641 
wire 

calculation, 622 

example, 623, 624, 625 
problems, 627 
specifications, 621 
lighting circuits, 621 
motor circuits, 622 
search-light circuits, 621 









Index 



969 



Slaby wave meter 
description, 904 

tuning closed sending circuit, 
910 
open sending circuit, 
911 

Slot, slots 

insulation, armature, 6-32-80 

generator, 230, 231 
insulation, armature, 100 K. W. 

generator, 245 

Sockets 

non-water-tight, 649 
instrument lamp, 654 
key, 649, 654 
keyless, 649, 654 

Socket ring 
variable speed gear, 391 

Solenoid 
brakes, 355 

band, 355, 356 

disc, 355, 357 
magnetic circuit, double, 128 
magnetizing force. 124 
stopped, 128 

Sparking 
brushes, 460 
limiting generator output, 198 

Specific 

conductivity, 46 
resistance, 36 
table, 37 

Specifications 

engines, 502, 503, 504, 505, 506 
generators, type 6-16-450-125, 
237, 238, 239, 240 
300 K. W. turbine- 
driven, 252, 253, 
254, 255 
motors, 291, 292, 293 
motor generators, 373, 374, 375, 
376 
gun-elevating equip., 446, 
447, 448 
switchboards, 563, 564, 565 
wire, size, 621 

Specific gravity 
secondary cells, 81 



Speed 

control of shunt motors, 267 
motors, relation of E. M. F., 

261 
reduction to normal, 466 
regulation by field change, 285 
relation to brush lead, 267 
relation to field of motors, 267 
separate controller rheostat, 

336 
tests, 736 
variation of armature, 472, 473 

Spider 

armature, 100 K. W. generator, 
242 

Spools 

insulation, 6-32-80 generator, 
232 

Spoud 

C. G. S. unit of acceleration, 
10 

Springs 

compression, disc brakes, 360 

Standard resistances, 702 

Stay light, 671 

Steam 

distribution in Gen. Elec. 

Form H-l engine, 516 
engines, 502 

early types, 502 
installation of fittings, 499, 500 
pressure, Gen. Elec. Form H-l 
engine, 514 
Gen. Elec. Form H-2 
engine, 529 
turbines, 546 
velocity, 548 

Steel 

melting point, 39 
Steel conduit, 655 

Storerooms 
care, 871 

Stuffing-box 
valve stem, Gen. Elec. Form 

H-l engine, 519 
valve stem, Gen. Elec. Form 

H-2 engine, 530 



970 



Index 



Sturtevant B. F. 

100 K. W. engine, 545 
motor, blower, 308 

armature, 310 

bearings, 311 

brush rigging, 313 

commutator, 311 

description, 308 

field coils, 310 

magnet frame, 309 

pole pieces, 309 

Sub-feeders, 630 

Sulphates 
secondary batteries, 86, 87 

Sulphuric acid 

secondary batteries, 75, 81 

Susceptibility 
magnetic, 115 
coefficient, 115 

Swinburne's test 
connections, 480 
example, 482 
instructions, 481 

Switch, switches 
care, 864 

commutating, 386 
contact fingers, 386 
cylinder, 386 
frame, 386 
shaft, 386 
terminals, 387 
conduit wiring 

5-ampere, single pole, 648, 
650 
with hood, 648 
25-ampere, double pole, 648, 

650 
100-ampere, double pole, 648 
50-ampere, double pole, dou- 
ble throw, 648, 650 
controlling panel, speed, 333 

field regulating, 333 
controlling panel, type U. S., 

328 
molding wiring 

5-ampere, single pole, 651 
25-ampere, double pole, 652 
50-ampere, double pole, 652 
100-ampere, double pole, 652 
50-ampere, double pole, dou- 
ble throw, 652 
non-water-tight, 649, 654 



Switch and receptacles 
conduit wiring, 648 
5-ampere, 648, 650 
with hood, 648 
25-ampere, 648, 650 
with hood, 648 
molding wiring 

5-ampere, single pole, 652 
25-ampere, double pole, 652 

Switchboards 
distribution, 574 

connections, 576, 577 

explanation, 575 
dynamo room, 574 

connections, 572, 573 
early types, 559 

instrument board, 560 
fire-control system, 817 
general, 558 
ground detectors, 571 

lamp, 571 

voltmeter, 571 
interior communication, 831 
parallel connections, 571 
small vessels, 560 
specifications, 563, 564, 565 
standard, 565, 566 

connections, 567 

explanation, 566 

front view, 568 

voltmeter connections, 569 
telephone, 751 

common battery, 753, 754, 
755 
elements of, 754 

magneto, 752 
telephone, ship, 789, 790, 791 

batteries, ringing, 792 
talking, 792 

care, 797 

circuits, ringing, 795 
talking, 795 

switch, plugless, 794 

wiring diagram, 792, 793 

Systems 
fire-control telephone, 814 
motor-generator, 373 
rotary compensator, 377 
Ward-Leonard, 363 

System of units 
C. G. S., 10 

derived, mechanical, 10 
practical, 16 



Index 



971 



Table, tables 

characteristics, incandescent 
lamps, 588 

electrochemical series, 54 

faults of generators and mo- 
tors, 724, 725, 726, 727, 728 

good conductors, 34 

insulators, 51 

melting points, 39 

partial conductors, 34 

remedies for faults of genera- 
tors and motors, 724, 725, 
726, 727, 728 

resistances, 38 

tests, incandescent lamps, 589 

wire, single, 616 

stranded, 617 
twin, 618 

Tandem-compound engine 

description, 507 

Tantalum 

filaments, 593 

Telegraph 

circuits, 768, 797 
engine, 768, 797 
helm, 768, 799 
wiring, 800 

Telegraphy- 
wireless, 872 

Telephones 

calling apparatus, 747 

circuits, 768 

common battery system, 749 

desk, 761 

induction coils, 746 

interior, 757 

central switchboard system, 
757 

common talking circuit, 757 

general intercommunicating 
system, 757 
local battery system, 747 
navy standard, 761 
receivers, 743 
simple connection, 738 
switchboards, 751 

ship, 789, 790, 791 
transmitters, 739 

Telephone system 
fire control, 814 

stations, 814, 815, 816 



Telephone system — Cont'd 
switchboard, 817 
telephone circuits, 818 
12-inch turrets, 819 

Temperature 
arc, 596 

coefficient of circuit, 44 
correction for copper conduc- 
tors, 41 
resistance coefficient, 40 
rise, in dynamo machines, 474 

calculation, 475, 476, 477 
variation with resistance, 39 

Terminals 

commutating switch, rotary 

compensator, 387 
controller, rotary compensator, 

386 
controlling panel, speed, 333 
controlling panel, type U. S., 

330 
primary cell, 55 

Test, tests 
armature resistance, 462 
chain ammunition-hoist motor, 

299 
dynamo machines, 456 
earth, 709 
heat, 736 

insulation conductors, 620 
interior communication cable, 

767 
lamp, 590 
lighting wire, 620 
magnetism, 735 
rotary compensator, 451 
speed, 736 
Swinburne's, 480 

connections, 480 

example, 482 

instructions, 481 
table, incandescent lamps, 590 

Testing set 

galvanometer, 685, 689 
resistance coils, 688 
service, 689 

battery, 691 

coils, 690 

commutator, 692 

connections and circuits, 691 

galvanometer, 690 

keys, 691 



972 



Index 



Testing set— Cont'd 
plugs, 706 

uses, 704 

checking ammeter, 709 

checking voltmeter, 708 

comparing E. M. F. cells, 
707 

measuring resistance, 705 
example, 706 

measuring battery resist- 
ance, 708 

measuring insulation re- 
sistance, 713, 714, 715 

measuring very low resist- 
ance, 706 
silver chloride cell, 689 

Testing set, Evershed, 695 
connections, 696 
instructions, 697 
magneto, 697 
needle, 697 

Theory 
application to practical appa- 
ratus, 257 
Curtis steam turbine, 547-553, 

inclusive 
electric generators, 154, 155 
motors, 256 

general principles, 256 

Thermal detectors, 896, 898 

Thermometers 

rise of temperature, 474 

Thermostats 
mechanical, 805 
mercurial, 804 

Thompson, S. P. 

determination E. M. F. around 
armature, 494 

Three-way boxes 

conduit wiring (see Junction 

boxes), 648 
interior fittings (see Main 

junction boxes), 650 
molding wiring, 649 

Three-wire system 

general explanation, 645, 646 

Time 

C. G. S. unit, 10 



Tin 

electrochemical series, 54 
melting point, 39 

Top lantern, 670 

Torque 

definition, 260 
expression, 261 
relation to speed, 263 

Towing lantern, 670 

Transformers 

continuous current, 444 
oscillation, 879 
principle, 149, 150 
rotary, 831 

Transmitters 

battle order, 810 

wiring, 813 
engine revolution, 801 

wiring, 801, 802 
engine telegraph, 799 

wiring, 799 
helm telegraph, 799 

wiring, 800 
telephones 

carbon, 741 
Blake, 741 
White, 742 

Cory, 778 

Edison, 740 

Holtzer-Cabot, 787 

Hughes microphone, 740 

Hunning, 740 

navy type, early, 777 

Truck light, 671 
care, 868 

Tune, tuning 

closed sending circuit 
Donitz wave meter, 909 
Fleming's wave meter, 910 
Pierce's wave meter, 910 
Slaby's wave meter, 910 

open sending circuit 
Donitz wave meter, 911 
Fleming's wave meter, 911 
Pierce's wave meter, 911 
Slaby's wave meter, 911 

receiving circuit 

Donitz wave meter, 914 
Pierce wave meter, 913 



Index 



973 



Tune, tuning — Cont'd 

wireless telephone, De Forest 
instructions, 922 
receiver, 929 
antennae, 930 
earth lead, 930 
pancake tuner, 929 
transmitter 
condenser, 927 
listening, 927 
microphone, 927 
primary spiral, 927 
secondary spiral, 927 
talking, 927 

Tungsten 

filaments, 593 

Turbines, Curtiss steam, 546 
specifications, 546, 547 
theory, 547 

Turret 

ammunition hoists, 405 
care, 854 
starting, 854 
stopping, 854 
directions for operating, 854 
elevating equipment, 397 
telephone circuits, 819 
turning equipment, 363 
care, 850 

equalizing load, 850 
lubrication, 851 
order of operation, 851 
motor, 301 
motor-generator system, 373 

connections, 376 
rotary compensator system, 

377 
variable speed gear, 390 

Twin conductors 
dimensions, 618 
insulation, 618 

Type, types 
A gaskets, 656 
A-l water-tight telephone, 780, 

781 
B-l non-water-tight telephone, 

783, 785 
C circuit breakers, 354 
C-3 water-tight telephone, 784, 

785 



Type, types— Cont'd 

F non-water-tight telephone, 

785, 786 
M. L. circuit breakers, 352 

care, 844 
M. Q. circuit breakers, 350 

care, 844 
M. P. generator, 6-32-80, 227 
motors, 293 

CB-15, 293, 294 

CB-24, 301 

CB-25, 295, 296, 297 

CB-27, 301 

CB-32, 303, 304 

CB-34, 306 

CR Form G, 307 

GE-800-E, 303 

Sturtevant, 309 

Underrunning 
generators, 585 

Unions 

conduit fittings, 655 

Unit, units 
acceleration, 10 
area, 10 

candle-power, 590 
C. G. S. 

capacity, 31 

current, 17 

E. M. F., 22 

length, 10 

mass, 10 

power, 24 

quantity, 18 

time, 10 
conductivity, 46 
derived mechanical, 10 

area, 10 

velocity, 10 

volume, 10 
electrical heat, 26 
electromagnetic resistance, 23 
E. M. F., 18 
force, 12 
international, 31 
magnetic field, 17 
magnetic pole, 16 
metric 
• length, 9 

mass, 9 

time, 10 
practical, 10 



974 Index 

Unit, units — Cont'd 
capacity, 32 
current, 18 
E. M. F., 22 
power, 24 
quantity, 18 
work, 26 

Use 

ammeters and voltmeters, 676 
example, 677. 678 



■I 



Valve, valves 
high pressure 

Gen. Elec. Form H-l engine, 

517 
Gen. Elec. Form H-2 engine, 
531 
low pressure, 

Gen. Elec. Form H-l engine, 

517 
Gen. Elec. Form H-2 engine, 
532 
steam, Gen. Elec. Form H-l en- 
gine, 516 
steam, tandem-compound en- 
gine, 509 
stems, 509 
stems, Gen. Elec. Form H-l en- 
gine, 518 
stuffing-box, 519 
throttle, Gen. Elec. Form H-l 

engine, 524 
throttle, Gen. Elec. Form H-2 
engine, 535 

Variable speed gear 

applicability, 396 
description, 390 

control screw, 390 

cylinder barrel, 391 

mid (or end) plate, 394 

shaft, 391 

socket ring, 391 

tilting box, 394 
efficiency, 396 

Varnish 

table of insulators, 51 

Vector diagrams 

component and resultant E. M. 
F., 433 

Velocity 

C. G. S. unit, 1Q 



!S, I 



Ventilation 

equipment, 418 

control panels, 420 
sets, care, 857 
brushes, 857 
location of safety devices, 

857 
lubrication, 857 
order of operating, 857 

Voice tube 
calls, 769 

Volt, volts 
lost, 181 
millivolt, 22 
practical unit of E. M. F., 22 

Volta, 22 

Voltage 

arc lamps, closed, 598 

open, 598 
audion, 928 
comparison, 

compound generator, 191 
separately excited generator, 

190 
series generator, 190 
shunt generator, 191 
relation continuous and alter- 
nating currents, 454 

Voltmeter, voltmeters 
calibration, 703 

connections, 703 
care in connecting, 679 
care in using, 679 
checking by testing set, 708 
connections on standard 

switchboard, 569, 570 
decreasing range, 704 
ground detector, standard 

switchboard, 571 
increasing range, 704 
measuring 
current, 698 

insulation resistance, 716, 
717 
connections, 716 
example, 718 
resistance, 699 
of, 700 

shunt windings, 720 
standard resistance, 701 
with ammeter, 700 
Weston, 680 

description, 680, 681, 682 



Index 



9T5 



Volume 

C. G. S. unit, 10 

Vulcabeston 
use, 52 

Ward-Leonard 

motor control, 363 

Warning signal 
circuits, 768, 808 
contact switch, 809 
wiring circuit, 810 

Water 

diamagnetic, 114 
table of conductors, 34 

Watt, watts 
apparent, 441 
converting to 

B. T. U. per sec, 28 

ergs per sec, 26 

ft.-lbs. per min., 26 

horsepower, 26 

joules per sec, 28 

kilogr. meters per sec, 26 
curve, 440 

practical unit of power, 24 
relation to horsepower, 26 

power factor, 442 
true, 442 

Watt hours 
secondary cells, 82 

Waves 

electromagnetic, 883 

analogy to sound waves, 886 

applied to wireless tele- 
phones, 919 

form, 884 

length, 884 

meters, 903 

properties, 884, 885, 886 

relation of frequency and 
wave length, 885 

Weight 

definition, 13 

Weston 

ammeters, 682 

portable, 683 
voltmeters, 680 

description, 680, 681, 682 

Wheatstone bridge, 686 
theoretical bridge, 687 



Wheel 
star, 



for controllers, 344 



Whip hoists 

diagram of connections, 411 
electrical connections, 410 
electrical equipment, 411 

White 

telephone transmitter, 742 

Winches (see Deck winches) 

Windings 
armature, 

100 K. W. armature, 244 

insulation, 245, 246 
field, generator 

6-32-80, 231 

100 K. W., 244 

service generators, 224 
insulation, service generators, 

224 
resistance of, tests, 460 
series, 6-32-80 generator, 232 
shunt, 6-32-80 generator, 233 

Wire, wires 
bell, 762, 763 

tests, 767 
binding 

armature, 100 K. W. genera- 
tor, 246 
service generators, 223 
lighting, insulation, 618, 619, 

620 
size, 616 
stranded, 617 

three (3) wire system, 645, 646 
two (2) wire system, 629 

Wire tables 

single conductor, 616 
stranded conductors, 617 
twin conductors, 618 

Wireless sets 

rotary converters, 454, 455 

Wireless telegraphy 
equation, 876 
principles, 872 

Wireless telephony 

De Forest system, 921 
principles, 915 
theoretical principles, 916 



/ 



3J r /£t>0 






976 



Index 



Wiring 
ammunition-hoist circuits, 826 
annunciator, 771, 772, 773 
battle and range order circuits, 

811, 813 
call bell, 770, 771 
cease-firing circuits, 828 
electrical interior communica- 
tions, 762 
engine revolution circuits, 801, 

802 
engine telegraph circuits, 799, 

800 
general, 628 

general alarm circuits, 807 
helm angle indicator, 803 

telegraph circuits, 800 

installation, 635 

conduit, 636 

molding, 636 

loop system, 630 

closet, 631 
parallel system, 631 

loop system, 632 
plan, lighting circuits, 629 
powder division circuit, 812 
range and deflection circuits, 

824 
salvo firing circuits, 824 
switchboard, ship's telephone, 
792, 793 
standard, 567 
telephone circuits to 12-inch 

turrets, 819 
warning signal circuits, 810 



>°i 



Wiring accessories 
care, 843 

Wiring appliances (interior com- 
munication) 
connection boxes, 830 
cut-out switches, 829 
push buttons, 830 
pear, 830 

non- water-tight, 830 
water-tight, 830 

Wood 
table of partial conductors, 34 

Wool 

table of insulators, 51 

Work 

C. G. S. unit, 13 
examples, 15, 29 
practical unit, 26 

Yoke 

adjusting, 251 
electromagnet, 126 
position, 100 K. W. generator, 
250 

Zinc 
constituent German silver, 35 
diamagnetic, 114 
electrochemical series, 54 
resistance, pressed, 38 
table of conductors, 34 
use, 35 



•i 






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